DECEMBER 28, 1916] 
INTERNATIONAL ELECTRIC AND 
MAGNETIC UNITS. 
HE U.S. Bureau of Standards has issued a use- 
ful and interesting critical résumé‘ of the prin- 
ciples underlying the establishment of the present inter- 
national system of practical electric and magnetic 
units, together with a survey of the various attempts 
that have been made ‘to ‘rationalise’? them so as to 
make the factor 47 one of less prominence in the 
equations most used in practice. —_ $ 
The international system of C.G.S. units is not 
strictly a C.G.S. system, for it is actually defined in 
terms of two arbitrary units, the international ohm 
and the international ampere, together with length and 
time. Nevertheless each unit in the system is the 
representative for practical purposes of the correspond- 
ing unit in the C.G.S. electromagnetic system, and 
differs from it only slightly. The small differences 
are determined by absolute measurements made from 
time to time. One of the advantages of the inter- 
national system is that it does not give undue promin- 
ence to magnetic pole strength; as Mr. Dellinger puts 
it: ‘The complexity,of the dimensional expressions of 
the electromagnetic system and its poor correspondence 
to the conditions of practice are in part due to its 
being based upon an unimportant phenomenon.” He 
points out that a free magnetic pole does not exist in 
Nature, magnetic pole strength does not appear in 
engineering formulz, and it is consequently a satis- 
faction to find«that it can be dispensed with in theory 
also. 
Magnetic units, however, are not entirely free from 
confusion, notwithstanding the casting into oblivion 
of the once useful but now unnecessary conception of 
the free magnetic pole. Gauss was a great man with 
an ugly name. Physicists and “ practicians”’ alike 
have always been partial to employing the names of 
great men for electrical and magnetic units (even if 
the great man in question had not been more par- 
ticularly identified with the quantity to be christened 
than with others of the same category), and ugly 
names for units have had a strange fascination for 
them. So “gauss” has been seized upon both for the 
unit of induction and for the unit of magnetising force. 
This double usage is recognised by the American 
Society for Testing Materials, and, provisionally, by 
the American Institute of Electrical Engineers, but 
Mr. Dellinger clearly voices the disapproval of the 
Bureau of Standards. It is true that the numerical 
equality of B and H in non-magnetic media, and their 
appearance as terms in the equation B=H+4zJ, both 
tend to encourage the idea that they are of the same 
physical nature, but ‘‘the argument that dimensional 
identity indicates physical identity is refuted by the 
example of energy and torque. Who would measure 
torque in joules or calories?’’ B, in fact, charac- 
terises the magnetised state of the medium, and H is 
the agency tending to produce that state, just as the 
deflection of a spring is physically different from the 
mechanical force producing it. There is no authority 
for considering » to be a purely numerical ratio. p is 
one of the two quantities (« and K) which are effective 
in the propagation of electromagnetic waves, and must 
therefore be an actual physical property unless K in- 
volves both the physical properties which are dynamic- 
ally necessary in a medium for the propagation of 
waves. The possibility of comparison is rendered 
worse by the fact that the name ‘‘ gauss” was tenta- 
tively adopted in 189s by the B.A. Committee on Elec- 
trical Standards as the C.G.S. unit of magnetomotive 
1 Scientific Papers of the Bureau of Standards. 
System of Electric and Magnetic Units.” 
Physicist, Bureau of Standards. 
Office, 1916.) Price ro cents. 
NO. 2461, VOL. 98] 
No. 292, *‘ International 
_ By J. H. Dellinger, Assistant 
(Washington: Government Printing 
NATURE 
337 
force. Mr. Dellinger suggests that the ‘* gauss”’ be 
retained as the unit for B only, or that it be avoided 
altogether. The “ gilbert’”’ has, been adopted as the 
C.G.S. unit of magnetomotive force, and the gilbert 
per cm, is already widely used as the C.G.S. unit of H. 
The C.G.S. unit of magnetic flux is the ‘‘ maxwell,” 
and B can always be called the maxwell per sq. cm. 
The attempts to ‘‘rationalise’’ the units to make 47 
less conspicuous date back to Oliver Heaviside’s pub- 
lications in 1882.7 His proposals involved, however, 
an entirely new set of practical units. Perry, Fessen- 
den, Fleming, and Giorgi followed with other proposals 
between 1889 and 1901, and the matter was. revived 
again by Ascoli last year,* and, finally, by Prof. V. 
Karapetoff. Prof. Karapetoff uses the international 
ohm and ampere as fundamental units, the ampere- 
turn as the unit of magnetomotive force, and the C.G.S. 
units for magnetic flux and induction. The system 
of ‘“‘ampere-turn”’ units is treated at some length in 
Mr. Dellinger’s paper, and the equations required to 
make the ampere-turn fit in with the units of other 
Magnetic quantities are given; but he concludes:by ex- 
pressing the opinior. that none of the proposed changes 
in some, or all, of the existing systems of international 
electric and magnetic units offer advantages sufficient 
to justify the confusion and inconvenience that would 
be involved, 
ARGENTINE METEOROLOGY .# 
Eo YipENCE of the activity and progress of the work 
carried on under the direction of Mr. W. G. 
Davis in the years preceding his retirement in March, 
1915, after thirty-five years’ service in the Meteoro- 
logical Department of the Argentine Republic, is con- 
tained in the undernoted memoirs. . 
In the work dealing with the ‘‘ History and Organ- 
isation’’ of the Oficina Meteorolégica, Mr. Davis 
gives a succinct account of the initiation and develop- 
ment of the service founded in 1872 by Dr. A. B. 
Gould, first director of the Cordoba Astronomical 
Observatory. In 1884, when Dr. Gould retired, there 
were fewer than twenty meteorological stations in 
operation. In igor the number had increased sixfold, 
with, in addition, 240 rainfall stations, while in rg14 
there were no fewer than 212 stations, of which forty- 
two were of the first class, i.e. provided with auto- 
matic instruments. The rainfall was then being re- 
corded at no fewer than 1930 points. The great strides 
made in the meteorological representation of the 
country during the period covered by the directorship 
of Mr. Davis is well shown on maps indicating the 
position of the various classes of stations in 1884, rgor,. 
and 1914. A Daily Weather Map was started in 1902, 
and is now based on reports from more than 200 
ordinary stations and 1350 rainfall stations, including 
observations from the neighbouring Republics, 
An excellent series of maps is given showing seasonal 
and annual values of all the elements of climate except 
cloud amount and humidity. A selection of the data 
on which these are based is given on pp. 154 to 181. 
2 The Electrician, vol. x.» p. 6 (1882); ‘Electrical Papers,” vol. i., 
PP. 199, 262, 432; vol. ii., pp. 543, 575 (1892). 
8 L'Elettroternica, vol. li., p. 731 (1915); Electrical World, vol. Ixvii., 
p- 876 (x916). 
4 (1) “ Servicio meteorolégico Argentino : Historia y organizacidn, con un 
resumen de los resultados.” (In Spanish and English.) Pp. 181-+maps and 
charts. (Buenos Aires, 1914.) (2) Anales, tomo xv., “Clima de Buenos 
Aires,” 2 parts. Pp. 1221. (Buenos Aires, 1912.) (3) Anales, tomo xvii., 
parte 1, “ Observaciones de las Islas Orcadas en los anos 1905 4 roto.” (In 
Spanish and English.) Pp. 720. (Buenos Aires, 1912.) (4) Anales, 
tomo xvii., parte 2, ‘‘ Clima de las Islas Orcadas del Sud. Discusidn de las 
observaciones meteorolégicas y magnéticas en la Isla Laurie.” (In Spanish 
and English.) Pp. vit+314+22 plates. (Buenos Aires, 1913.) (5) Boletin 
No. 4, ‘‘ La termodinamica de Ja atmésfera terrestre, desde la superficie hasta 
el plano de desvanecimiento.” Por F. H. Bigelow. (In Spanish and 
English.) Pp. 142. (Buenos Aires, 1914.) (6) Boletin No. 5, ‘* Resultado 
de las observaciones del magnetismo terrestre.” Por Luis G. Schultz. (In 
Spanish and English.) Pp. 12+4 plates. (Buenos Aires, 1914.) 
