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Full text of "Recent Actions Taken By The Symbols, Units, And
Nomenclature
"
See other formats
Recent Actions Taken By the Symbols, Units,
and Nomenclature (S.U.N.) Committee
Of the International Union of Pure and Applied Physics (I.P.U.)
in Reference to C.G.S. Magnetic Units
BY ARTHUR E. KENNELLY*
Fellow and Past President of the A.I.E.E.
Synopsis.—Iin reference to the C.G.S. magnetic units, a brief
historical outline is presented of the actions taken by international
electrical congresses from 18938 to 1904, and by international tech-
nical and scientific unions from 1904 to 1982. Emphasis is laid
on the results of the S.U.N. Committee meeting of July, 1932, as
the latest development. l
The present status of international agreement on C.G.S. magnetic
units is unofficially presented, in the light of the historical back-
ground. |
Turning to future possible developments, certain questions are
PURPOSE AND SCOPE
HE aim of this paper is to offer a brief unofficial
T account of what international actions have recently
been taken in the matter of C.G.S. magnetic units,
tending to eradicate some of the ambiguities that have
pervaded magnetic literature during the last thirty
years, and especially the actions in this direction taken
during 1931-1982, by the International Electrotechnical”
Commission (I.E.C.) and by the International Physical
Union (I.P.U.), together with the present nomenclature
status of these C.G.S. units, and what little yet remains
to be done, in order to secure general international
agreement. It will be seen that this is essentially a mat-
ter of names, definitions and nomenclature; since no
changes have been suggested in the C.G.S. units
themselves.
The second part of the paper relates to magnetic units
in the practical, or volt-ohm-ampere series. Here rela-
tively little has yet been accomplished. In order to
extend this series into a complete comprehensive sys-
tem, it appears to be necessary to secure agreement
upon two very important questions: (1) Shall the mmf of
a coil of NI ampere-turns be 47NTI practical units, or
NI ampere-turns simply? (2) What unit of length shall
be embodied in the system? Suggestions are advocated
upon both questions.
HISTORICAL OUTLINE SINCE 1927
In a paper entitled Magnetic-Circuit Units, read
before the Midwinter Convention of the A.I.E.E.,
January 29th, 1930, the writer had the privilege of
presenting a historical outline of magnetic units from
*Harvard University and Mass. Institute of Technology.
17. See bibliography for numbered references.
Presented at the Winter Convention of the AJI.E.E., New York,
N. Y., January 23-27, 1938.
pending for consideration, by either or both committees, in order to
clear up any outstanding differences of international opinion over
magnetic units in the classical C.G.S. system.
In order to convert the existing series of practical electromagnetic
units (ohm, volt, ampere, coulomb, farad, joule, watt, henry and
pramazwell) into a complete system, international agreement must
first be reached upon the two outstanding questions:
(a) Subrationalising (4T NI or NI for mmf).
(b) The unit of length to be adopted (meter or cm). Suggestions
are offered along both these lines.
1861 up to that date. It will therefore not be necessary
here to reconsider the history of the subject prior to
1927, when the International Electrotechnical Com-
mission (I.E.C.) prominently entered the fidld.
The I.E.C. was projected in 1904, at the International
Electrical Congress of St. Louis, and was inaugurated
at London in 1906. It has been continuously in existence
since that time. It has national committees in some
twenty countries. Each such national committee is
composed of representatives of its national government,
local scientific and technical bodies, as well as various
electrical industries. The general secretariat is in
London; but the presidents, of which there have been
eight up to this date, are elected successively from the
various countries. Each national committee has its own
president, secretary, and other officers.
The work of the I.E.C. is divided among nineteen
separate advisory committees, each with its own presi-
dent, and with a secretariat located in one country.
Some advisory committees have delegates from a rela-
tively small number of countries. Others have delegates
from all or nearly all countries. Through the London
central office, the different advisory committees convene
at suitable times and places, to work out their own
problems. As and when they arrive at agreements, they
notify the central office, and report to the next plenary
meeting of the I.E.C. asa whole. The plenary meetings
are held about once in two years, and there have been
nineteen in all thus far, distributed in time and place
among twelve cities. The work of a plenary meeting
consists largely of receiving reports from the various
advisory committees, and of adopting them, as a body,
by vote. The I.E.C. also receives and passes upon
applications for the holding of international electrical
congresses, in countries which desire to hold them.
The tasks undertaken by the various advisory com-
mittees relate broadly to electrical engineering, and
647
33-52
648
especially to the standardisation of machinery, appara-
tus, specifications, methods and tests entering into
electrical applications. In advisory committee No. 1
on “Nomenclature,” definitions, symbols and units
have been dealt with at various times.
At the plenary meeting of 1927, in Bellagio and
Rome, a proposal was introduced by the Italian national
committee, relating to magnetic units; both C.G.S. and
practical. After some unsuccessful discussion, it was
referred to a special subcommittee on “Magnetic
Units” of the Advisory Committee on Nomenclature,
for study and report, with a personnel group of rep-
resentatives from seven countries. This subcommittee
worked over the subject until 1929, without being able
to reach an agreement, owing to the marked differences
of opinion presented among the various national com-
mittees involved. The subcommittee reported in
1929, recommending that, in view of the large range of
differences in opinion, the subject should be discussed
in the national committees and placed upon the agenda
for the next plenary meeting at Oslo in 1930. The
subject was, in fact, ventilated in the technical press of
several countries, in advance of the meeting of 1930.
The main difficulties in reaching agreement centered
around the unit? name gauss, which had been adopted
in 1900, at Paris. Magnetic literature all over the
world, between 1900 and 1930, showed much confusion
and ambiguity as to the meaning of this name. Some
writers used it exclusively for the unit of flux density,
or induction density B. Others used it exclusively for
the unit of magnetising force, or magnetic intensity H;
while yet others used it for both B and H indiscrimi-
nately. Moreover, some authoritative text books
held that the quantities B and H were physically differ-
ent, in which case, of course, the unit name gauss could
only be applied to one; but to which was not certain.
Other equally authoritative text books held, on the
contrary, that the quantities B and H were physically
identical; so that the gauss if applied to one, would
also be applicable to the other. There was no middle
ground between these two positions, and the first aim
of the international subcommittee dealing with the
subject, was to decide which of the two contentions
should be supported.
When the magnetic units subcommittee met (June,
1930) in Scandinavia, its numbers were increased to
include twelve countries, and its name was changed to
Section B of the Nomenclature Committee, dealing
with Electric and Magnetic Magnitudes and Units,
(E.M.M.U.). After discussion, it was voted unani-
mously to adopt the convention, that for electro-
technical purposes, the quantities B and H should be
regarded as being physically distinct; so that in a
vacuum, or free space, B = uH, where us is the space
permeability, and is not a mere number, but a physical
quantity having dimensions; furthermore that in the
case of magnetic substances, B = uH, where u is the
absolute permeability of the medium, with the same
KENNELLY
Transactions A.I.E.E.
dimensions as uo; but the relative permeability of the
medium would be u/uo a mere number.
These conventions having been adopted, the E.M.-
M.U. committee was able to deal speedily with other
C.G.S. magnetic units which had offered difficulty.
The following list of units and names was agreed to,
either unanimously or by considerable majorities.*
(a) For the C.G.S. Magnetic Unit of magnetic flux
6, the name maxwell
(b) For the C.G.S. Magnetic Unit of flux density
B, the name gauss
(c) For the C.G.S. Magnetic Unit of magnetising
force H, the name oersted
(d) For the C.G.S. Magnetic Unit of mmf the name
gilbert.
The name maxwell had already been adopted in 1900
at Paris, for magnetic flux 6, as reaffirmed here under
(a). The name oersted was applied to the unit of H,
partly to indicate that, by convention, the name gauss
being assigned to the unit of B, was not applicable to
the unit of H. In America, the name oersted had been
applied provisionally to the unit of reluctance @, since
1900; but without international authorisation. The
assignment of the name oersted to the unit of H as in
(c), leaves the C.G.S. magnetic unit of reluctance with-
out a name, for the present.
The E.M.M.U. Committee also adopted the name
pramaxwell for the unit of magnetic flux © in the
practical series (108 maxwells) and the prefix pra as a
general means of designating a practical unit derived
from a C.G.S. unit.
The preceding resolutions, and others not directly
within the scope of the C.G.S. units, were reported to
the plenary convention of the I.E.C. at Oslo, and by
it unanimously adopted, July 9th, 1930.
Following upon the publication of the I.E.C. actions
on the C.G.S. magnetic units, comments appeared in
the scientific and technical press of various countries.
In general, these comments were favorable; but some
adverse criticisms also appeared, mainly directed to
two points:
(a) That names of savants should not have been
given to C.G.S. units.
(b) That the name gauss should not have been given
to the unit of B; but to that of H, in conformity with
the usage of terrestrial magnetic observatories.
In regard to (a), the Paris Congress of 1900 had
assigned the names maxwell and gauss to C.G.S. units,
in view of the decision of the Congress of 1893, at
Chicago, that working magnetic units should be kept
within the C.G.S. system.
In regard to (b), it was pointed out that in view of
the confusion in literature over the use of the name
gauss, the I.E.C. convention necessarily brought em-
barrassment to some group of workers; but that the
number who were in the habit of using the gauss for B
seemed to be much greater than those accustomed to
using the gauss for H. Moreover, the earth’s magnetic
June 1933
field is measured in air, which being a feebly magnetic
medium, may be regarded as developing a flux density
B under the action of the magnetic intensity H al-
though, from a numerical standpoint, there would be
no appreciable difference between the air values of H
and B. . Terrestrial magnetic observatories are also
accustomed to report their magnetic measures in terms
of a special unit the gamma or y, equal to 1/10° oersted,
and there had been no suggestion of disturbing this
usage.
In view of any or all differences of opinion elicited
by the publication of the I.E.C. Oslo resolutions, ar-
rangements were made and announced early in 1931,
to hold a special meeting of the E.M.M.U. committee
at London, in September 1931, to review these C.G.S.
recommendations.
ESTABLISHMENT OF THE S.U.N. COMMITTEE BY THE
INTERNATIONAL PHYSICAL UNION
The International Union of Pure and Applied
Physics (I.P.U.), met at Brussels in July 1931, and
established for the first time, an international com-
mittee on “Symbols, Units and Nomenclature,”
(S.U.N.). The 8.U.N. committee elected as its Chair-
man Sir Richard Glazebrook, and as its Secretary,
Dr. E. Griffiths. Since electro-technical units fall
within the scope of the 8.U.N. Committee, the I.E.C.
extended an invitation to the I.P.U., to aid in the task
of seeking international agreement on electric and
magnetic units, through the coöperation of the 8.U.N.
and E.M.M.U. committees. This invitation was ac-
cepted, and the 8.U.N. Committee was invited to have
its members attend and take part in the London
E.M.M.U. meeting, already scheduled for September
1931. The S.U.N. Chairman and Secretary were able
to attend, and also the General Secretary of the I.P.U.,
Professor H. A. Abraham.
ACTIONS OF THE LONDON MEETING oF E.M.M.U.
COMMITTEE, SEPTEMBER 1931
At the opening of the E.M.M.U. meeting in London,
September 18th, 1981, the President of the I.E.C.,
Dr. A. F. Enström, and the General Secretary, Mr.
C. LeMaistre, took part.” The national committees
of ten countries were represented:—Denmark, France,
Germany, Great Britain, Holland, Italy, Norway,
Poland, Sweden and U.S.A.
The agenda proposed by the American committee
in February 1931, were then adopted as basis for
procedure.
The first proposal on these agenda: (la) was con-
sidered:
“that the C.G.S. magnetic units and their ac-
cepted names, as fixed at the Oslo plenary
meeting, should remain undisturbed”’
This proposal was voted unanimously, two countries,
however, abstaining, (Holland and Italy).
The next proposal (1b), related to a series of practical
SYMBOLS, UNITS, AND NOMENCLATURE COMMITTEE
649
magnetic units, based on the pramaxwell, or volt-second
as adopted at the Oslo meeting, with the ampere-turn
as unit of mmf. After a long discussion, during which
considerable difference of opinion was revealed, it was
voted to defer action on these practical units until the
national committees should have had further oppor-
tunity of examining the question.
On the particular question, however, of a practical
unit of mmf F, and whether a coil of N turns, carrying
a steady current of I amperes, should be taken as
§ = 4r (NI) units, or merely 5 = (NI), a vote was
called for on the proposition that it should be § = 4 7
(NI). Three countries were in favor of the proposition
(France, Holland and Italy); while four voted against
the proposition: (Germany, Great Britain, Sweden and
U.S.A.). Two countries, Norway and Poland, ab-
stained from voting. It is evident that there is much
difference of opinion over this important question.
Item II of the agenda, on a conventional interpre-
tation of reactive power in unspecified, alternating-
current right-angle triangles, was next considered; t.e.,
whether + 7 vars should be taken as signifying induc-
tively reactive power, or the reverse, when the basis
of the diagram is not specified.
It was unanimously voted that a convention should
be adopted; but that decision as to the direction, should
be deferred until a new and definite American recom-
mendation should be presented.
Some difference of opinion had been raised as to
whether the particular direction recommended in the
agenda (+ 7 P, for inductively reactive power), was the
more advantageous choice.
Item III of the agenda related to a proposed inter-
national adoption of the prefixed “ab”? and “stat,”
applied to a practical unit, for the designation of a
corresponding unit in the C.G.S. magnetic, or in the
C.G.S. electric system, respectively. These prefixes
have been and are in use, to some extent, in America;
but have never been internationally adopted.
For lack of support to the proposal, no action was
taken and the meeting adjourned.
MEETING OF THE S.U.N. COMMITTEE IN PARIS
The 8.U.N. Committee issued a questionnaire, in
December 1981, to physicists and physical societies
in different countries, on “Electrical Units,” calling
attention to certain ambiguities in the definitions of
fundamental electric and magnetic quantities entering
into the C.G.S. system, and inviting opinions as to
how these ambiguities might be eliminated, in order
to arrive at international agreement. The replies to
this questionnaire were collected. In view of the con-
siderable number of physicists assembling in Paris
during the week July 5th-12th, to attend the Inter-
national Electrical Congress of 1932, the S.U.N. Com-
mittee called an informal meeting in Paris on July
9th, to discuss these questions, and especially the
C.G.S. magnetic units.
650
The meeting was held under the chairmanship of
Sir Richard Glazebrook, Dr. E. Griffiths of the British
National Physical Laboratory (N.P.L.) being the
Secretary. Nineteen persons, from eight countries,
attended. The actions taken were informal, in the
sense that the voting was not by countries; but by
individuals.
The following propositions were adopted, either
unanimously, or by considerable majorities:
1. Any system of units recommended must retain the eight
internationally recognised practical units: joule, watt, coulomb,
ampere, ohm, volt, farad, henry.
2. The C.G.S. system of units is suitable for the physicist.
3. A system of practical units ineluding the above eight
quantities, is derived from these by multiplying the C.G.S. unit
by appropriate powers of 10.
4. That M. Abraham at the request of the conference, should
prepare for consideration by the Commission, a preliminary
report on the fundamental units.
5. The system of magnetic units may be based on the follow-
ing two methods as alternatives:
(a) The force between two elementary magnet poles,
(Coulomb).
(b) The force between two elements of current,(Ampére).
6. B and H are quantities of different nature.
7. The factor 47/10 should be retained in the definition of
magnetomotive force.
The following table of electromagnetic quantities,
which in accordance with suggestions received, has
KENNELLY
in electrotechnical journals.
Transactions A.I.E.E.
and that the unit names maxwell, gauss, gilbert and
oersted for #, B, § and H are respectively satisfactory.
If these conventions continue to receive support, the
ambiguities and confusion which have pervaded inter-
national magnetic literature during the past thirty or
forty years, should disappear. The only group whose
current practise seems to be embarrassed by the con-
ventions, is the terrestrial magnetic group, who have
long been accustomed to employ the gauss for H. As
has already been pointed out, however, these important
scientific researches in terrestrial magnetism deal almost
exclusively with magnetic phenomena in air, at ordinary
temperatures and pressures. The numerical difference,
between B and H in air under such conditions, is ad-
mitted to be only about one part in three millions;
which is insignificant in the existing stage of measure-
ment precision in terrestrial magnetism. There can be
no present confusion in magnitudes, when the gauss
in air is mentioned. Moreover the use of the gamma
in terrestrial magnetic work is not interfered with.
In the United States, The I.E.C.-I.P.U. Conventions
have been accepted by the National Bureau of Stand-
ards, the Society for Testing Materials, various
committees of the A.I.E.E., and the U.S. National
Committee of the I.E.C. Endorsements have appeared
They are also used, to
the exclusion of all others, in the “Report on Proposed
TABLE I—ELECTROMAGNETIC QUANTITIES
C.G.S. units Volt-ampere units
Quantity designated Symbol Equation Name Unit Defining units
dë
TN 5 seg ek e a e ee oe ee: a —E...... Maxwell........... -10° MIRWEUS: 24% 24 25 e4 we Volt-second
Induction or flux density..................00 2 re J BMS 58o. Gauss............0-. 10° gauss................. Volt-sec /em?
l 1
Mmf round a circuit 2.2... 0.0... 00. ees f a ere F =4rNI......... Gilbert or oersted-cm. To gilbert or
vis ampere-turn......... Amperes
Magnetizing force or field strength..... ...... i; ere S B . cos e.ds = F ..Oersted.............. 2: oersted or
=472NI 10
amp turn percm.....Amperes per cm
T
10° gauss lt- 2
Permeability... ....s esunsun a nno Heas u =., eee Permeability......... ee ee en eg O O
H oersted
been revised since the meeting, is now proposed for
adoption by the British representatives.
PRESENT STATUS OF THE C.G.S. MAGNETIC UNITS AS
THE RESULT OF I.E.C. AND I.P.U. ACTIONS
It will be seen from the preceding 8.U.N. recom-
mendations and table, that there is agreement in all
essentials between the findings of the I.E.C. and I.P.U.
committees, so far as concerns the C.G.S. magnetic
units. Both have recommended the convention that
the quantities B and H should be taken as different,
amp turn/cm
mw
American Standard Definitions of Electrical Terms,’
sponsored by the A.I.E.E., and recently published
(August 1932). Up to the present date (November
1932), no objections seem to have appeared in North
American literature to the I.E.C.-I.P.U.-C.G.S. con-
ventions, and the only complaints raised have been
that the previously existing C.G.S. unit name for re-
luctance has been removed, without designating any
substitute. As a minor detail of symbology, however,
an objection has been raised to the use by the I.E.C.
of the symbol uo for space permeability. This symbol
June 1933
has been used to some extent in America for ‘‘initial
permeability;” 7. e., the “normal permeability when
both the magnetising force (H) and the induction (B)
are vanishingly small.” If it should be desired to retain
the symbol yu, for initial permeability, space permea-
bility, or the permeability of vacuum, might be
represented by some other symbol, such as w.
MATTERS OUTSTANDING FOR CONSIDERATION IN
RELATION TO C.G.S. UNITS
Up to this point in the paper, the writer has en-
deavored to present an unbiased historical picture of
what the I.E.C. and I.P.U. have been able to do for
clearing international understanding of magnetic uni-
tology. In what follows, opinions and suggestions are
submitted, in the role of an advocate rather than of a
historian. |
It is often supposed that the well known relation
B = uH gausses, which connects magnetic flux density
with permeability and magnetising force, extends only
to magnetic media, and has neither theoretical nor
practical interest when free space, or non-magnetic
media, are considered. Further examination shows,
however, that this is too narrow a view to fit the facts.
In a vacuum, free space, or non-magnetic media, the
equation becomes B, = uH gausses; where B, is the
space flux density, and uo the space permeability. In
the C.G.S. magnetic system, the numerical value of uo
is arbitrarily made equal to unity, and for purposes of
mere computation, the equation might just as well be
B = H, in which form it sometimes appears in text
books and which would justify the view that B and H
are physically identical. But in the C.G.S. electric
system (commonly called the electrostatic system), the -
value of u, necessary to satisfy the equation is uo = 1/c?,
where c is the velocity of electromagnetic wave propa-
gation, or nearly 3 X 108 meters per second. In any
other system of electromagnetic units, a value of u,
differing from unity must be used, even for purposes of
computation, except in the Maxwell Q.E.S. (quadrant-
eleventh gram-second) system. A few cases appear in
the following table:
TABLE II
Values of uo Satisfying the Space Relation Bo = uoH for Various Systems
No. System of units Value of po
1. .Classical or Maxwellian C.G.S. magnetic unrational-
1.0
TSO can thaia Gey en oe a ee ae 1/(0.9) X 10-2!
3..M.K.S. (meter-kilogram-second) unrationalised ..... 10-7
4..M.K.S. (meter-kilogram-second) rationalised....... . 4r X 1077
5..0.G-S.S. (em-gram-seven-second) unrationalised .... 10-9
6..C.G-8.S. (cm-gram-seven-second) rationalised...... 4r x 10-9
7..Maxwellian Q.E.S. (quadrant-eleventh-gm-second)
unrationalised................ ee ee re eee 1.0
It has been pointed out in several countries that there
are several classical C.G.S. magnetic formulas which
should include uo, in order to acquire general applica-
SYMBOLS, UNITS, AND NOMENCLATURE COMMITTEE
651
tion. One of these is B, = uH, often written B = H
for nonmagnetic media. This question of inserting uo
in certain classical C.G.S. magnetic formulas where it
generically belongs, ought to be considered by the
E.M.M.U. Committee, independently of the I.E.C.
Convention that u. has dimensions of some kind, other
than a mere number. It has been claimed that uo as
space permeability, is a fundamental physical constant.
The Ausschuss fiir Einheiten und Formelgréssen has
named it the “Induction Constant.”
QUESTIONS TO CONSIDER IN RELATION TO THE
PRACTICAL UNITS
It will probably be generally admitted that the
difficulties in the way of rectifying the C.G.S. magnetic
units internationally are small compared with the
difficulties of reaching agreement over the extension
of the practical series of units into a complete compre-
hensive system. No changes have been made in the
classical C.G.S. Magnetic system, which was adopted
by the Paris Congress of 1881, endorsed, beyond any
question of modification, by the Paris Congress of 1900,
accepted by the Electrical Committee of the Inter-
national Committee of Weights and Measures and was
also endorsed by the S.U.N. Committee at the Paris
meeting last July, under item (2) above referred to.
On the other hand, the practical units are now nine in
number: the ohm, volt, ampere, coulomb, farad, watt,
joule, henry and pramaxwell or volt-second. These form
a one-to-one series; but not a complete system. We
may define a comprehensive practical system as any
system of units susceptible of universal scientific
measurements and computations, which includes the
nine practical units as constituent elements. In order
to complete the practical series into a practical system,
certain additions must be agreed upon. These missing
elements are of great importance. The first elements
of the series are now more than fifty years old, and the
completed system may last for centuries. Great care
is therefore needed in choosing the best new elements;
because while the choice is pending, we. can carry on
all our work in the C.G.S. system.
QUESTION OF PRACTICAL UNIT OF MMF AND
SUBRATIONALISATION
Probably the first question to consider is the defini-
tion of the practical unit of mmf. Shall it be the 1/47th
part of an ampere-turn or just an ampere-turn?
This is the old rationalisation question first raised by
Heaviside in the seventies. He showed that ration-
alised C.G.S. units would be much simpler to think
with, and work with, than those of the classical C.G.S.
system; although the method by which he advocated
rationalising, would have meant changing the magni-
tudes of nearly all the existing practical units and
standards, and was quite unacceptable. Later on, it
became known how to subrationalise a system; 7. e., to
obtain the advantage of rationalisation through in-
652
creasing the unit of space permeability 47 times, and
diminishing the unit of space inductivity 47 times.
Karapetoff has recently presented a simple means of
analysing any system of electromagnetic units, (setting
aside the units of length and mass), in terms of five
significant constants: namely, (n) the ratio of electric
flux to the charge producing it; (p) the corresponding
ratio of magnetic flux to the pole producing it; (k) the
ratio of themmf of a coil to the current-turns producing
it; (€o) the space inductivity and (uo) the space permea-
bility. He proceeds to show that a certain simple
relation must hold among these five parameters in any
n
workable system €o uo È = een E
The three
parameters n, p, and k are indicated to be arbitrary
numerics; while the product e€, uo has the same dimen-
sions as the inverse square of c the light velocity. On
the basis of this analysis, we may define a system as
subrationalised, when the ratios n and p are each equal
to unity. If k is also unity, so much the better. In
both classical C.G.S. systems (magnetic and electric),
as well as in the Q.E.S. system, the ratios n and p are
each equal to 47. This makes unit pole produce 4r
maxwells, and a corresponding numerical relation be-
tween electric charge and flux; whereas the basic idea
should be that unit pole is a maxwell, and a unit charge
is unit flux. So great is the advantage of this simplifica-
tion that, as we all know, a large part of modern electro-
magnetic theory is carried on in the Heaviside-Lorentz
rationalised C.G.S. system, and not in the classical
C.G.S. system.
Various writers have indicated the simplification in
working formulas brought about by subrationalisation.
The books and papers thus far written in systematised
practical units (Giorgi, Bennett, Karapetoff) have
used n = p = k = 1.
The proposition to adopt 4r NI as the mmf ofa coil
in the practical system was raised in the E.M.M.U.
London meeting of September 1931. At that time,
the vote was 4 to 3 against the proposition, (two
countries not voting). At the S.U.N. Paris meeting
of July 1932, a similar proposition was carried by a
vote of 10 to 3; so that the E.M.M.U. was in favor of
rationalising, by a small majority; while the S.U.N.
was opposed to rationalising, by a large majority.
The question should be thoroughly examined in all
KENNELLY
Transactions A.I.E.E.
countries and only finally settled, one way or the other,
by a large majority. There is a danger that if the vote
is not nearly unanimous, there may be a schism in the
practical system, just as there has already been a schism
in the C.G.S. system. We should thus face the danger
of having a classical practical sect and a rationalised
practical sect.
The arguments raised against practical rationalisa-
tion seem to be weak. One has been that certain well
known relations now existing between the C.G.S. mag-
netic and C.G.S. electric systems would be lost if
rationalisation were adopted. Granting that this is
true, there can be no bad result in the case considered,
because there will be a practical magnetic system; but
no practical electric system. The duality of the present
classical C.G.S. system will fortunately disappear from
the proposed completed practical system. It has also
been urged that the product €o uo which is 1/c? in the
C.G.S. system, will have some other value in the prac-
tical system, when rationalised. This may be true in
the general case; but is not true in either of the pro-
posed completed practical systems. See Table III,
Nos. 6 and 8.
Table III, prepared in accordance with the Karapetoff
analysis, brings a number of different systems into
comparison. Nos. 1 and 2 are the classical C.G.S.
systems. No. 3 is the rationalised Heaviside-Lorentz
system, No. 4 is the Maxwell practical system, as
drawn up by its author and unrationalised. No. 5
indicates how that system would appear if rationalised.
No. 6 is the Giorgi system, in the rationalised form
presented by its author; while No. 7 is how it would
appear unrationalised. No. 8 is the system for which
there are a number of claimants, among them Dellinger,
Bennett and Karapetoff. No. 9 is the same in unration-
alised form, first suggested by the Committee on Units
and Standards of the A.I.E.E. in 1891; although the
implications as to the unit of mass (10’ gm) were not
then apprehended.
It has always been urged against rationalisation that
if the factor 47 is taken out of mmf it will have to be
inserted in permeance and reluctance in order to main-
tain the magnetic flux @ unchanged in magnetic-circuit
Ohm’s law. The argument is that no advantage would
be gained by the process. It must be remembered,
however, that in the great majority of practical mag-
netic-circuits, magnetic material such as iron or steel
TABLE III
L M T
No. System cm gm sec n p k €o Mo
| nee ene eee Classical C.G.S. electric unrat................2.. ccc eee eee | re L- E | Pr r E 4m... 4r.. 1 .1/c?
PEE Classical C.G.S. magnetic unrat........... teeta eg eens aie L... 1 1l.. 4m... Am... 4x.. 1/c? 1
e RO EES Heaviside-Lorentz rat... 0.00000 ee eee 1 A 1 Pee eee L eeu aera Ea 1 1
re ae Maxwell practical Q.E.S. unrat..........0. 00.00.00. cee eee 10?..... 10-1! oe 4q...... 4m... 4r.. 1/c? 1
EREE Maxwell practical Q.E.S. rat......... cece ee ee ee a 108... 107 ces | ee eee D can ces | ee 1 1/4 xc? 4r
Go caedeens Giorgi M.K.S. fab o5.9'sd one ado ah urranna ee eee 107..... 10° Seuec2 | EIEE 1 T nas 1 . 107/4 r c?...4 7/10"
Toen ORE E E E E E E 10?..... 108 oe oe Agr... 4r Aw... 107/2... 107
Se eae Dell. Benn. Kar. C.G.S.S. rat... 0. cc ees Lee O'n we aatuce s rene 1 eee 1 109/4 r c?...4 7/109
9 CS aod ob cores Fans koe Sess He bake es Sees l See. 107 1l.. 4T... E 4r 5 a 10-°
June 1933
has to be employed, and that the relative permeability
of this material has to be included in the computation,
usually through the use of a table or curve sheet. Since
the relative permeability factor, has, therefore, ordi-
narily to be inserted, it is easy to include the 47 factor
in the table or curve sheet, so as to have no necessity
for introducing the 4r term separately. There is thus
an economy of time and effort involved in the ration-
alised process of magnetic-circuit Ohm’s law. The
Ohm’s law formula is, moreover, only one of many in
which the 47 factor appears. In nearly all of them the
rationalised formula is distinctly simpler than the un-
rationalised formula. |
A real objection to rationalisation would be the
divergence of the practical system from the unration-
alised basic C.G.S. magnetic system. The main
question to be decided would be whether the very real
advantages of rationalisation are counter-balanced by
the disadvantage of departure from the corresponding
classical C.G.S. formulas.
QUESTION OF THE UNIT OF LENGTH IN THE PRACTICAL
SYSTEM
In addition to, but independent of the question of
rationalisation, comes the question of the unit of length
to be used. The choice of the length unit logically |
determines the units of area and volume. It has been
shown by various writers, that in order to conform with
energy and power requirements, (the joule and wait),
there are only two units within the range of serious
consideration; namely, the meter and the centimeter.
Theoretically the quadrant is also included; but it is so
large as to be out of discussion. The quadrant as a
unit of length, exceeds the earth’s radius. The square
quadrant, as a unit of area, is about one-fifth of the
surface of the globe, and the cubic quadrant, as a unit
of volume, is of the same order as the earth’s volume.
No one has had the courage to propose these units
seriously, and it does not appear that Clark Maxwell,
who discovered the relation of the units in this system,
regarded them as of a workable character.
The centimeter is a more convenient and familiar
unit of length than the meter for most electrical engi-
neering purposes. On the other hand, however, it is
linked with a large and awkward unit of mass: 10’
grams, or ten metric tons. It is a question, therefore,
whether in the general use of the practical system, for
purposes other than electromagnetic, the disadvantage
of this large mass unit might not outweigk the advan-
tages of the centimeter.
It has been contended that neither the M.K.S. nor
the C.G.S.S. system is permissible as a scientific unitary ©
structure, for the reason that in neither of them is unit
density the same as that of water. The unit density in
the M.K.S. system is the kilogram per cubic meter,
which is 1,000 times less than that of water. The unit
density in the C.G.S.S. system is 10 tons per cubic
centimeter, which is 10’ times the density of water. It
SYMBOLS, UNITS, AND NOMENCLATURE COMMITTEE
653
is of course desirable to have the unit of density iden-
tical with that of water, from a practical point of view;
but the failure to meet this condition probably is not
so serious as some have claimed. For practical pur-
poses, what we need is a table of specific gravities, or
the densities of substances divided by the density of
water. Once such a table has been prepared, the
absolute density of water becomes of relatively small
importance. It seems doubtful whether any practical
system, otherwise acceptable, should be rejected be-
cause its unit of density is not that of any familiar
substance.
Bibliography of Magnetic-Circuit Units
Subsequent to that contained in author’s A.J.E.E. paper of
January 1931. (Magnetic-Circuit Units Adopted by the I.E.C.)
1. Bennett, Ed., Comprehensive Systems of Units for Universal
Use. Trans. A.I.E.E., April 1930.
2. Lombardi, L. “Comitato Consultivo di elettricità annesso
al Comitato Internatzionale dei pesi e misure.” L’ Hlettrotecnica
A.E.I., Dee. 15, 1930, Vol. 17, No. 35.
3. Mailloux, C. O. “La question du ‘gauss’. La question de
la Responsabilité-Les diverses définitions de l'expression ‘flux
magnétique’.” Revue Gén. de l’El., Paris, Vol. 29, Jan. 24, 1931,
pp. 125-135.
4. Kennelly, A. E., Magnetic-Circuit Units Adopted by the
I.E.C., ELECTRICAL Ence., N. Y., Feb. 1931, p. 133.
5. Brylinski, E., “Sur le Système d’ Unités,” Revue Gén. de
l’ Elect., Paris, Vol. 29, pp. 209-213, Feb. 7, 1931.
6. Budeaunu, C. I., “La question des Grandeurs et Unités
Electriques et Magnétiques,” Inst. Nat. Roumain, No. 11,
Feb. 1931, pp. 23.
7. Kennelly, A. E., “The Convention of Equidimensional
Electric and Magnetic Units.” Proc. Nat. Ac. Sc., Washington,
D. C., Vol. 17, No. 3, pp. 147-153, March 1931.
8. Van de Well, G. J., “De Magnetische Einheden in 1900
te Paris en in 1930 te Stockholm,” De Ingenieur, Holland, 1931,
No. 35, pp. 8.
9. Kennelly, A. E., ‘“‘Rationalised versus Unrationalised
Practical Electromagnetic Units,’ Proc. Am. Phil. Soc., Vol.
70, No. 2, pp. 1038-119, Apr. 1931.
10. Kennelly, A. E., “The Oersted Considered as a New
International Magnetic Unit.” The Scientific Monthly, N. Y.,
April 1931.
11. Brylinski, E., “Sur le Système M.T.S.V. de Mesures,”
Rev. Gén. de l Elec. Vol. 29, pp. 733-740, May 9, 1931.
12. Blondel, André, “Comparaison entre les Systémes prati-
ques d’Unités électromagnetiques,”’ Rer. Gén. de VEL, May 16,
1931, Vol. 29, pp. 771-783 and May 23. 1931, pp. 814-825.
13. Brooks, H. B., The Unit of Electrical Resistance. Past
History and Impending Change.” Proc. A.J.H.E#., June 1931.
14. Blondel, A., “Remarques sur la subrationalisation des
unités pratiques,” Rev. Gén. del’ Elec. Paris, Vol. 29, June 1931.
15. Spooner, Thomas, “C.G.S. Magnetic Units Should Re
Standard,” The Elec. Journal, Aug. 1931, pp. 475-476.
16. Mitkevitch V., “Sur les Unités Magnétiques Pratiques.”
Proc. Ac. des Sc. de ’ U.S.S.R., Leningrad, Aug. 1931, pp. 1-9.
17. I.E.C. Document R. M. 97. Unconfirmed Minutes of
Meeting of E.M.M.U. Committee, Sec. B Av. Com. No. 1 on
Nomenclature, held in London, Sept. 18, 1931, pp. 4.
18. Howe, G. W. O., “The Nomenclature of the Fundamental
Concepts of Electrical Engineering.” J.H.E. Journal Scottish
Centre, Chr’s. Address, Vol. 70, No. 420, Dee. 1931, pp. 54-61.
19. Questionnaire issued on ‘‘Electrical Units,” by the S.U.N.
Committee of the I.P.U., Dee. 1931, pp. 2.
20. Kennelly, A. E., “The Present Status of Magnetie-Circuit
654
Units,” Prac. Jap. Inst.
March 1932, pp. 197-209.
21. Page, Leigh, “Electromagnetic Equations and Systems of
Units,” Physics., Vol. 2, No. 4, pp. 289-302, April 1932.
22. Wennerberg, John, “A Study of Physical Quantities in
Mechanical and Electrical Engineering,’ Swedish Elect. Com.
1932, pp. 38.
23. Germani, D., “Choix d'un Système d'unités Electromag-
nétiques.” Rev. Gén. del El., Vol. 32, pp. 39-50, July 9, 1932.
24. Andronesen, P., ‘‘Notes sur la question des Grandeurs et
Unités électriques et magnétiques.” Com. Elect. Roumain,
No. 13, 1932.
El. Engrs. Tokyo. Vol. 52, No. 524,
25. Bodea, E., “Un Système d’Unités pratiques doté de 4
Dimensions Fondamentales.” Com. Elect. Roumain, No. 14,
1932, pp. 35.
26. Vasilesco-Karpen, N., “Sur une nouvelle Exposition des
Phénomènes Electromagnétiques. Inutilité de la Notion de
Masse Magnétique,” Com. Elect. Roumain, No. 15, 1932, pp. 9.
27. Budeanu, C. I., “Sur les Principes Fondamentaux con-
cernant la Structure des Systèmes d’Unités et les Définitions des
Grandeurs en Electrotechnique.” Comité Elect. Roumain, No.
16, 1932, pp. 16.
28. Karapetoff, V., A General Theory of Systems of Electric
and Magnetic Units. A.J.E.H. Trans, Sept. 1932, pp. 715.
29. Kennelly, A. E., Recent Developments in Magnetic Units,
ELECTRICAL ENGINEERING, N. Y., May 1932.
30. Kennelly, A. E., “Actions of Electrotechnical Com-
mission on Names for Meenstic Units.” A.S.A. Bulletin, N. Y.,
June 1932, pp. 183-184.
31. Cotton, A., “Les Noms des Unités Magnétiques.”
Int. € Elect., Paris, 2nd Sec., July 1932, pp. 7.
32. Joly, Louis, ‘“L’Etat actuel de la Question des Unités
Electriques et Magnétiques,” Cong. Int. d Elect., Paris, July
1932, pp. 17.
33. “Report on Proposed American Standard Definitions of
Electrical Terms.” Sponsor A.I.E.E. Glossary of 3,300 Terms,
pp. 204, Aug. 1932.
34. Kennelly, A. E., “Standardisation of Metric Magnetic
Units.” Industrial Standardisation, Nov. 1932, Vol. 3, No. 11,
pp. 284-285.
Cong.
Discussion
George A. Campbell: I should like to call attention to the
practical results of the conventions set forth in this paper, as
shown by a document which the paper says has used these con-
ventions to the exclusion of all others. I refer to the “Report on
Proposed American Standard Definitions of Electrical Terms”?
sponsored by the A.I.E.E., with Doctor Kennelly as chairman
of the committee in charge. It was published last August with
a request for comments and suggestions.
Section 35 on “Units and Systems of Measurement” of the
Group 05 on “General Terms” defines 5 ¢.g.s. systems with 27
of the c.g.s. units, next a practical system with 9 practical units,
and finally an international system with 10 units. From these
definitions the engineer can learn, for example, about the ohm,
the abohm, the absolute ohm and the international ohm, but
nowhere is he told what ohm is actually used in our shops. The
engineer may be impressed with the multiplicity of ¢.g.s. systems
but he cannot fail to find them confusing. Even if he is wise
enough to skip the first four-fifths of the text and start in with
the international system, he finds that every international unit
definition refers him, in the end, to the corresponding absolute
unit. This first leads him back to the definitions of the practical
units, and then on back to the long, involved definitions of the
e.g.s. units and ¢.g.s. systems.
Would it not be far better, in definitions intended for the
electrical engineer, to define first, as briefly and directly as
1. Report No. 2 of A.I.E.E. Standards.
KENNELLY
Transactions A.I.E.E.
possible, the units which actually are used by the machine shop
in the manufacture of electrical equipment, by the retail shop in
the sale of electrical equipment, and in the shop talk at all
A.I.E.E. conventions? The engineer could then get what he
really needs without encountering the artificial difficulties which
were invented when the leading scientists hardly had the grasp
of electrical units which the youthful radio amateur now seems
to have. It would, however, not be feasible to omit all reference
to ¢.g.s. units because the electrical engineer will unfortunately
encounter them in the literature of physics. This calls for the
familiar conversion table to enable him, upon encountering any
¢.g.s. unit, to translate it into the shop unit which he really
understands. |
What I am suggesting is that in this A.I.E.E. glossary of terms
relating to units both the order and the emphasis should be
inverted. Put the shop ohm, the shop volt, the shop ampere-
turn and the shop volt-second first and not the c.g.s. units.
There would be no reference to ¢.g.s. units before the table at
the end of the glossary. The shop units would be the basie units
and the ¢.g.s. units would appear as derived units.
If you agree to this, it seems to follow that in his training the
engineering student should start at once with the shop units.
Then much later he would be introduced to the conversion table
for use when, and only when, he encounters a ¢.g.s. unit in the
literature. This plan should work perfectly with boys who have
become familiar with the shop electric units as radio amateurs
and household electricians. If this is the best procedure with
students of engineering, it is, I believe, also the best procedure
with high school and college students of physies. It seems quite.
certain that if a generation of engineers and physicists were
trained in this way, they would continue to think and write in
terms of shop units, and ¢.g.s. units would soon become of his-
torical interest only. This, it seems to me, is a goal devoutly to
be worked towards, and the present an opportune time for ener
neers to assist in accelerating the process of education.
Referring again to the A.I.E.E. electrical definitions: under the
“International System of Electric and Magnetic Units,” on page
34, occurs thestatement, ‘‘The International Committee of Weights
and Measures has decided to discard these units in the near future”
in favor, it is implied, of the absolute practical units, as announced
in the technical literature. This also calls for inversion, in my
opinion.2 Why? One among several reasons is this: the absolute
practical units and all ¢.g.s. units lead to formulas which are in-
fested with 47°’s and the 47’s are an unmitigated nuisance in
the shop, laboratory and study. The international ohm, am-
pere-turn, mechanical watt shop system is necessarily free from
these 47’s and such a system is ‘‘much simpler to think with and
work with,” as Doctor Kennelly says. I wish there were time to
take up Doctor Kennelly’s paper point by point, but in the in-
verse order of presentation, and show how this inversion simplifies
the subject and automatically eliminates one by one the diffieul-
ties which he sets forth. I refer especially to: “. . . the difficulties
of reaching agreement over the extension of the practical series of
units into a complete, comprehensive system,” including the
meter and ampere-turn, because it requires dropping the density
unit and the 47 of the c.g.s. electromagnetic system; “. . . the
ambiguities and confusion which have pervaded international
magnetic literature during the last thirty or forty years.”
. certain ambiguities in the definitions of fundamental electric
a magnetic quantities.”
To speed the adoption of the shop units as the dermal: pre-
ferred, universal system, the legalizing acts for metric and elec-
tric units, in the United States and other countries, should be
2. I cannot see, from the paper under discussion or from other reports of
the deliberations of international committees, that the great advantages of
relegating the c.g.s. systems to history in favor of a single, preferred system
of units, based on the meter, kilogram, second and shop ohm, have ade-
quately been considered by, or even clearly presented to, any of these
committees. Many of their votes, therefore. seem to me to lack finality.
June 1933
consolidated, revised and amplified. That the required changes
are small is illustrated by the accompanying table.’
A DEFINITIVE CHOICE OF MECHANICAL, ELECTRIC, AND
MAGNETIC UNITS SUITABLE FOR A LEGALIZED SYSTEM
Symbol and
. Unit name defining
Quantity (bracketed names to be shortened) equation
1 length............... INV sa cckateesa beware a aa L
2 OQCbss ede cd seen ees [square meter] = square meter...... S = alo
3 volume.............. stere = cubic meter............... V =LS
4 055 |: ae ee enano en SOCONG ss ebaee dep eeoe iva eb 6 OES T
5 POWER... anaana Wati 05 2 ond he hp ek er r we P
6 energy...... SIOU Oost nS ie ee Scobie a de ee eae W =PT
T POPC 6 oss cewek cbeaws [joule per meter].................. F =WL-1
8 pressure............. [joule per meter per square meter]..p = FS-t
9 mass................ [kilogram]. ccs ccd kas ecwsaaee a iveen M = Fa"
10 density.............. [kilogram] per stere................ d =My-}
11 electricity............ COMMOMID® 24:2.4.24 6 oka s 66 S94 bE
12 electric current....... ampere*..... 0.0.20. .00 cece eee eee I =QT"
13 electric potential...... VOLT eo cae ene pee eos E = Wọ-
14 electric capacity...... PAPA Seah aie de ded anann n 6 dl a etd C =QE-!
15 electricresistance.....0hm..............0 00 cee cee eee R =EI-!
16 electric conductance. .mho................ 0000 cc eee ees G =IE-
17 electric inductance....henry...............00 000 cece £ =RT
18 magnetomotive force. .ampere-turn*...............-..00- Ff = NI
19 magnetic flux......... volt-second*..... a Gos a Rs ened 6 =HT
20 reluctance............[ampere-turn per volt-second]....... R = Fp-
a = acceleration in meters per second per second.
*The five starred units are to be about one-fiftieth of one per cent smaller
than the corresponding international units.
The general adoption of these units should make it unnecessary
to become familiar with more than one system of units. This
would release human effort and soon eliminate the waste and
confusion which are a necessary consequence of our present
multiplicity of systems. Although the proposed single system of
units merely is a selection. and a re-alignment of present units, it
is not a patchwork expedient. It would sweep away at one
stroke all of the major difficulties set forth in Doctor Kennelly’s
paper.
Doctor Kennelly follows the international committees in con-
sidering that the classical ¢.g.s. magnetic system has been “‘en-
dorsed, beyond any question of modification, by the Paris Con-
gress of 1900.” The literture of physics actually shows, however,
that physicists do not consider the c.g.s. electromagnetic system
of units suitable for all their needs. Theoretical physicists have
substituted the Heaviside-Lorentz systems. Experimental
physicists actually make great use of wattmeters, ammeters and
voltmeters, together with the farad, ohm and henry. Funda-
mentally, the choice today is between ¢.g.s. authority and free-
dom to use the units which actual experience has shown to be
“simpler to think with and work with than those of the classical
c.g.s.”’
C. L. Dawes: Professor Kennelly’s paper gives a very concise
and yet comprehensive presentation of the developments and the
present status of the I.E.C. and associated committees in the
matter of the standardization of the c.g.s. magnetic units, both
in their dimensional relations and in nomenelature. Likewise,
the paper states that although practically unanimous agreement
has been reached in the retention of eight of the practical units,
yet names and even definitions have not as yet been assigned to
the other practical units such for example as mmf.
Progress has been made in that definite names have been
assigned to the c.g.s. magnetice units of flux, flux density, mag-
netizing force and magnetomotive force. Moreover, distinction
3. This table is taken from the manuscript of a paper under preparation.
The same units have been discussed in ‘“‘Three Superfluous Systems of
Electromagnetic Units” Physics, Vol. 3, No. 5, November 1932, pp. 230-239,
and “A System of ‘Definitive Units’ Proposed for Universal Use” Science,
Vol. 61, April 3, 1925, pp. 353-357. l
SYMBOLS, UNITS, AND NOMENCLATURE COMMITTEE
655
between the controversial units of B and H decisively is indicated
in their being assigned the respective names of gauss and oersted.
Also the troublesome question of the dimensions of permeability
u appears to be settled by convention in a very rational manner.
However, so far the c.g.s. unit of reluctance is not named;
it would seem highly desirable that a name be assigned to this
unit, not only to complete the nomenclature of these related
units, but also it is convenient to refer to a unit by name. The
name itself is not material so long as it is in general harmony
with electrical and magnetic nomenclature. It is the appro-
priate custom to name the units for savants and the name Weber
appears to be the best adapted to this magnetic unit. In the very
early days the name Weber was used as the name of the practical
unit of quantity and later as the name of the practical unit of
current; in more recent years it has been used unofficially in this
country as the name of the practical unit of flux, but the names
‘“‘voltsecond” and ‘‘pramaxwell,’’? make the name Weber no
longer necessary for the unit of flux. Hence the name Weber
appears to be available and could be well recommended as the
international unit of reluctance in the ¢c.g.s. system.
It also would seem highly desirable that all the remaining
magnetic and electrical units of the practical system be defined
and named. This system is the most used by engineers and
yet there has been little or no attempt to give names and defini-
tions to the magnetic and electrostatic units (except henry and
farad). In this respect I am in substantial agreement with Doctor
Campbell.
I believe, however, that the factor 47 should be retained
in the practical unit of mmf. This is in accord with proposition
(7) adopted by the S.U.N. committee in Paris in 1932. Al-
though a practical system should lean towards usefulness rather
than toward a rational and fundamental derivation, it is ques-
tionable if the factor 477 does produce any more inconvenience
when it appears in the numerator than it does when it appears
in the denominator either in the physical dimensions of the
magnetic circuit or in the permeability of vacuum. The author
recommends the ampere-turn as the unit of mmf, stating that
in engineering uses of magnetic materials their properties are
given as data and curves in which the permeability factor is
included, so that the 47 term in the denominator causes no
inconvenience. This same condition has existed for a long time
even under present conditions where the ¢.g.s. unit of mmf
having 47 in the numerator is used. As is well known it has
long been customary in scientific work of all kinds to plot the
flux density as a function of the ampere-turn per unit length.
Hence so far as such data or curves are concerned, it seems im-
material whether 477 appears in the numerator or in the denomi-
nator.
Furthermore all the present units of the practical system have
a definite relation to the fundamental ¢.g.s. system, the unit of
length being 10° em and the unit of mass 10-" gram. Elimina-
tion of the 47 factor in the unit of mmf will break this rational
relationship between these two systems, which I believe increases
confusion and is thus highly undesirable.
With several years’ experience, it appears to me that the so-
called confusion which the 47 factor produces, even among
students, is exaggerated greatly and is far out of proportion to
the efforts being made to eliminate it. The physical picture of
a unit charge or unit pole emitting 477 lines in a medium whose
absolute permittivity or whose permeability is unity is simplicity
in itself. In fact, to my mind this picture is a much more rational
one than attempting to visualize a unit charge or a unit pole
emitting only a single line and in a medium whose permeability
is 477. Moreover, the unit charge and the accompanying 47
lines lend themselves very readily to the very fundamental work
and potential relationships which are necessary in the derivations
of electrostatic potentials and capacitances.
Only very recently I asked two of my classes one of which
was composed of students who had only just begun seriously
656
the study of magnetic and electrostatic units, whether or not
the 47r lines emanating from unit poles or charges, was at all
bothersome. They unanimously stated that this convention was
very clear to them, in fact was much clearer than the unit line
per pole or unit charge. In fact, it has long been our experience
that students who are beginning electrostatic and electro-
magnetic studies have become greatly confused in attempting
to use text books where the ampere-turn and the unit line per
unit charge conventions are used.
Hence, it is in accord with my experience that the retention
of the 4r term in the practical unit of mmf would simplify the
understanding of magnetic relationships rather than confuse
them.
I am heartily in sympathy with Doctor Camphbell’s ‘‘defini-
tive” system and the simplicity which it implies, with the
possible exception of the unit of mmf just discussed. However,
I do not believe that the two fundamental c.g.s. systems should
be discarded or even thrust too far into the background, since
their units are derived in a simple manner from very fundamental
postulates; moreover, even if the “‘definitive’’ or an equivalent
system were legally adopted, I believe that these two funda-
mental systems still would be found to be very useful in certain
types of scientific work.
S. L. Gokhale: The paper divides itself into two parts:
1. A summarized history of the subject up to the present date.
2. Recommendations by the author as to further changes.
The first part contains a table of symbols and units (Table I)
suggested by the S.U.N. Committee, and recommended by them
for adoption. Doctor Kennelly agrees with the opinions of this
committee except on the question of rationalization; that is,
Doctor Kennelly stands for omission of the factor 47 in the equa-
tion F = 47 NI, while the S.U.N. Committee has decided to
retain it by a vote of 10 to 3.
Table I, column 3, contains what seems to be the defining
equations of the concepts in column 1, although they are not
specifically called by that name. Construing them as defining
equations, we find that their sequence is the reverse of that of
the scheme adopted by the I.E.C. and A.S.A. The I.E.C. and
A.S.A. first define m the magnetic pole strength. From this
they derive H and from H, F and from 3, J. The S.U.N. on
the other hand first define J and from this they derive F, and
from 5, H. Therefore, the agreement between the I.E.C. and
the I.U.P. (International Union of Physics represented by the
S.U.N.) as stated by Doctor Kennelly appears to apply to the
names of the units and their magnitudes. I hope that it will be
possible to work further with a view of arriving at an agreement
as to the sequence of the definitions.
With reference to the omission of 47 in the equation F = 4r],
and its transfer to the equation By = 47H, it may be conceded
that a large number of scientists favor the omission on the basis
of the dimensional conception of permeability, but the point
still is unproved.
The practical advantages of omitting 47 are more apparent
than real. For instance, in machine design where the magnetic
circuit is partly air and partly iron, the 477 cannot be eliminated
from the computation, for if it is suppressed in the calculation
of the iron part of the path, it will reappear in the air part. In
only a few instances, such as design of transformers without
leakage, can the 47 effectively be suppressed.
There are other cases in which, though the 47 does not enter
into the numerical computations, has yet to be ineluded in the
new form of the equation, and it is possible that it may be for-
gotten, until the old practices are forgotten and new practices
formed. For example, in transmission line calculation, engineers
would have to use the formula
2ul1
Ar
d
log ——- (where u = 4T)
r
KENNELLY
Transactions A.I.E.E.
in place of the present formula
d
2u1 log —— (where u = 1)
r
without the 47r.
The best policy under the present situation, is a policy of
compromise, which permits both parties to hold to their re-
spective views, without interference from the other party. The
decision of the I.E.C. in 1930 was the best possible compromise
under the circumstances. It permitted one school of thought to
assume the physical identity of B and H and to use the equation
B = H for space. This equation, though not obligatory to the
opposite school, is permissible for them on the hypothesis that
Ho has been given arbitrarily the value of 1. The compromise
also permitted followers of the dimensional conception of per-
meability to use separate names for the units of B and H.
Such a policy, though not obligatory to the non-dimensional
scheme is quite permissible. This situation might have continued
indefinitely without a conflict between the two schools until the
question of dimensional character of permeability and the conse-
quent difference in the physical nature of B and H could definitely
be settled. An attempt to introduce 47 into the equation
B, = 47H at this time would compel the followers of the non-
dimensional school to abandon the idea of B and H being physi-
cally identical, together with the equation B = H. It seems to
me that in proposing the change Doctor Kennelly is now going
against the spirit of that compromise, which governed the
decision of the I.E.C. in 19380. He admits, however, that the
change should not be made on the basis of a narrow margin of
votes as in the I.E.C. resolution of 1931, (R.M. 97).4
With reference to the substitution of the meter for the unit
of length in the practical system, while there may be theoretical
reasons for advocating this, I feel that in practise it only would
add further confusion to the present condition by ending in
giving us a third system in addition to the present two.
Hans Lippelt: During the discussion of the paper the use of
“shop units” in preference to scientific units has been advocated.
We do have shop units already, and I think this is a good op-
portunity to point out that some of them are bad. For illustra-
tion I wish to refer to the lb, which is often used in the shop as
the unit of the mass. But it is utterly wrong to do so. The
unit of the mass is lb-ft-! see?. If that term is too cumbersome
for practical use, then let us find a short name for it and a
symbol.
In going over the whole list of shop units, others also will be
discovered which cannot bear scrutiny in the light of logic and
accuracy. (For instance secondfeet, secft, is used for cubic feet
per second.) IJ think that all such faulty units should be amended
to become a true expression of their physical meaning. When
short and new names for such units become necessary, exact
definitions should accompany them.
Such a purging process should, indeed, be extended also to
our technical seript. It is customary to write sin-!z* to express
an angle œ whose sine is x, a method which is not compatible
with the definition of a negative exponent as given in mathe-
matics. Under this mathematical definition
sin-'z is equivalent to
ine x
and to nothing else.
If internationalism in the language of science and engineering
is not objectionable, but striven for, then we might just as well
accept the method as used in Europe.
4. Unconfirmed minutes of Meeting Section B on Elec. and Magnetic
Units of Comm. No. 1, held in London, Sept. 18, 1931.
*The reader may answer that I have myself used this wrong method
of writing. See A.I.E.E. Trans., Feb. 1926, p. 408, col. 2, last line. My
manuscript was correctly written. I had to change these mathematical
terms to the customary form, to render my paper acceptable to the
committee.
June 1933
They write ares in z for an angle (arc), œŒ, whose sine is z.
Ar Sin y
or Ar Sin y
W. I. Slichter: In this paper there are two matters of very
great interest to teachers of electrical engineering because they
involve the setting up of two new conventions, different from
previous practise and because it is the duty of the teacher to
prepare the future generations of engineers to accept and use
these conventions.
The first is the question of the algebraic sign and the vector
representation of reactive power and explicitly: shall inductive
reactive power be designated by + j and drawn upward from
the horizontal axis in vector diagrams? Either sign or direction
‘may be justified mathematically and scientifically depending
upon whether we take current or voltage as our reference vector.
for the hyperbolic angle (area), V whose hyper-
bolic sine is y. |
The paper indicates that the international committee prefers
a positive sign and upward direction for inductive reactive power,
which means taking current as reference vector. This is probably
quite satisfactory to those engaged in communication engineer-
ing. But those engaged in power engineering are dealing almost
entirely with nominally constant potential circuits with one
voltage common to all the circuits of the network and they
therefore naturally think of voltage as the reference vector.
In this case an inductive load means a lagging current and this is
so common that we frequently hear the terms “lagging load”
and “‘lagging power factor” where lagging means inductive.
Thus these people would naturally prefer the negative sign and
the downward vector for inductive power and the converse for
anti-inductive or capacitative reactive power. The final choice
primarily is one of suiting the habits of the majority of users
or that which will involve overcoming the least amount of mental
inertia.
The other question involves taking the constant 47 or 0.47
out of the magnetomotive force and putting it into the reluctance
in the formula for the flux in a magnetie circuit. This again
easily is justified scientifically if we ignore the very early de-
velopment of the art, but more important, this change would
put the law for the magnetic circuit in a form similar to that for
the electric circuit and the dielectric circuit and make for uni-
formity and therefore for clarity, logic, and ease of teaching.
Moreover, this is done already in most practical applications
for every one of our magnetization curves of magnetic steels is
plotted between flux density and ampere-turns and not gilberts
or 0.477 ampere-turns. Here the mu and the 0.47 are made part
of the reluctance or reluctivity of the material and the curves
give us immediately the ampere-turns which is the quantity of
practical interest, and not gilberts. If this change were adopted
we would have the three outstanding relations in electrical
engineering expressed in a similar manner:
NI 1
Qo = — = ——_—_
R 0.4 THA
E pl
I = P R = 7
E 1
e 8 = -KA
A. C. Seletzky: Whether or not + 7 vars or — j vars should
be considered as representing inductively reactive power in
unspecified alternating current right-angle triangles will probably
be decided on the basis of whichever usage predominates in
present practise. Both forms may be justified from the view-
point of mathematical consistency. In view of the fact that
+ jz has been internationally accepted for some years to repre-
sent inductive reactance, inductively reactive power in the form
of /?(j7z) would call for a positive sign, current being considered
SYMBOLS, UNITS, AND NOMENCLATURE COMMITTEE
657
the axis of reference. On the other hand if the voltage were used
as the reference axis, inductively reactive power in the form,
E? (— 7b), would require a negative sign.
In spite of the fact that capacity loads are encountered in
practise, I have observed that engineers generally think sub-
consciously of reactive power as inductive when it is unspecified,
by sheer weight of its more frequent occurrence. Since we
generally label quantities, which occur more frequently on one
side of an arbitrary line of demarcation as positive, the use of the
plus sign to represent inductively reactive power would seem to
be the more convenient form. An analogous situation is present
in the consideration of positive angles as those which are drawn
counter-clockwise from the positive axis of abscissas. Invariably
when one is demonstrating anything involving an angle in space,
one begins by drawing an angle in the first quadrant counter-
clockwise from the real axis: it is very probable that this usage
grew from manual convenience in drawing angles in this manner
and then led to the general acceptance of such angles as positive.
It seems that a similar condition obtains in the case of reactive
power and that inductively reactive power, from the standpoint
of convenience alone, should be considered positive.
A. E. Kennelly: Doctor Campbell has well pointed out the
advantages of a single system of units over the existing multitude
of systems. He advocates extending the present series of nine
international practical units (ohm, volt, ampere, ete.) into a com-
plete comprehensive and so-called absolute system, embracing
the meter, kilogram and second, with no separate electrostatic
system, and with the ampere-turn as the official unit of mmf.;
1. €., With the system subrationalised. His “Definitive System,”
substantially the same as the Giorgi system, would be a great
boon, if it could be used both in physics and in engineering, to
the exclusion of all other systems. In detail, there is some ques-
tion whether the international ohm should be taken at its existing
value; or whether it should be first brought more nearly into
agreement with the so-called absolute ohm of 10° abohms; but
this is a subsidiary question, outside of immediate discussion.
Professor Dawes points out that there is need for a name to
be assigned to the c.g.s. magnetic unit of reluctance, now that the
oersted has been taken for the unit of H. There are many who
agree with him. It is to be hoped that a name for the c.g.s.
magnetic unit of reluctance may be internationally agreed upon
and adopted.
Professor Dawes supports Doctor Campbell’s definitive sys-
tem; except that he wants it left unrationalised, like the existing
c.g.s. magnetic system. It was Heaviside and Lorentz who
showed the marked advantages of rationalisation; so that a large
part of electromagnetic theory is today written in the Heavi-
side-Lorentz ¢.g.s. system, instead of in the classical ¢.g.s. sys-
tem, owing to the simplification thereby effected. There are
thus two sects among basic electromagneticians; namely, the
e.g.s. classicists and the c.g.s. rationalists. The question will
have to be settled internationally, sooner or later, whether the
applied electromagneticians, using practical magnetic units, are
to be classicists or rationalists. It is not a question of what is
right or wrong; but as to the relative balance of advantages. No
classicist should be foreed to use rationalised units against his
will, and reciprocally. In view of the existing schism in the basic
literature, and of the considerable difference of opinion that
exists among engineers and technicians in regard to the practical
units, it looks at present, as though we might have to recognize
the existence of both classical and rational practical units; 2. e.,
both of the ampere-turn and of the ampere-turn/47, and allow
both these sub-systems to continue side by side, until inter-
national opinion shall have crystallized in favor of one of them;
when the other can be formally discharged. This is virtually the
state of affairs today in the basic c.g.s. world literature. Not
only are opinions on this question of subrationalisation different
among electrotechnicians in different countries; but there appear
also to be differences of opinion in each of nearly all countries.
658
Mr. Gokhale points out that we still are unable to decide on
scientific grounds, whether space permeability Ho has or has not
dimensions. We probably will all agree with him on this. There
are good authorities on both sides of this vexed question. Ulti-
mately, of course, there can be only one answer. Space permea-
bility Mo either is a mere number, or it is not a mere number.
The question is of less importance to the engineer than to the
physicist; but neither engineers nor physicists can use their
symbols, units, or definitions logically, without coming to a con-
ventional agreement upon the question. In the present state
of our knowledge of electromagnetism, it probably is better to
adopt an international convention, even if it should later be
proved wrong, than to carry on indefinitely the confusion of the
last thirty years. Thus far, we have had an agreement both in
the I.E.C. and in the I.P.U. on the convention that Mo has
dimensions, and is not a mere numeric.
Mr. Gokhale also properly draws attention to the need of
standardizing internationally the definitions of our magnetic
quantities. It is very desirable to have this done. The defini-
KENNELLY
Transactions A.I.E.E.
tions we still cling to are based upon the classical conceptions of
magnetic poles, consisting of magnetic point sources. Most
physicists admit the validity of these concepts and of the defi-
nitions resulting therefrom; but less artificial and more acceptable
definitions might be arrived at on the basis of concepts of mag-
netic flux, obtained from the researches of Ampère, Faraday and
Helmholtz.
Professor Slichter has drawn attention to the desirability of
having an international convention as to the interpretation of
right-angle power triangles when they do not specify the meaning
of lagging power. Should lagging power, or — j power, be taken
to mean inductively reactive power, or the reverse? Here again
is a need for a convention, and not a decision as to right or wrong.
He favors lagging power going along with lagging current.
General opinion among engineers seems to agree with him. Mr.
Seletzky, however, seems to be of the opposite opinion. There
probably is no large majority of opinion on this question; but it
should be settled as a convention, for general convenience among
engineers, and to avoid confusion.