414 



NA TURE 



[August 30, 1900 



A' 



UNITS AT THE INTERNATIONAL ELEC- 

 TRICAL CONGRESS. 



T the suggestion of Prof. Hospitaller, Section I. of 

 '- the Congress agreed that the following should be 

 the members of the Commission on Units :— Messrs. 

 Ayrton (Great Britain), De Chatelain (Russia), Dorn 

 (Germany), De Fodor (Hungary), Eric Gerard (Belgium), 

 Hospitaller (France), Lombardi (Italy), Kennelly (United 

 States) ; and at the first meeting of the Commission, on 

 August 21, which was attended also by Prof. F. 

 Kohlrausch and Sir W. Preece— whose names had been 

 added to the list of the Government delegates for Ger- 

 many and England— a report presented to the Congress 

 by the American Institute of Electrical Engineers was 

 taken into consideration. This report had been drawn up 

 for that Institute by a committee appointed for this 

 purpose, and it contained the following resolutions : — 



(i) We consider that it is necessary to give names to 

 the absolute units in the electromagnetic and electro- 

 static systems, as well as convenient prefixes to designate 

 the decimal multiples and submultiples of these units in 

 addition to those already in use. 



(2) The International Congress of Electricians, which 

 will take place this year in Paris, should be invited to 

 choose the names and the prefixes. 



(3) A great advantage would be gained by a rational- 

 isation of the electric and magnetic units, and the Con- 

 gress should be invited to find ways and means to obtain 

 such a rationalisation. 



The proposition to rationalise the units — that is, to 

 change them so that the coefficient \n should not appear 

 — was withdrawn by Dr. Kennelly on behalf of the 

 United States ; as well as the suggestion regarding the 

 employment of prefixes, and it was resolved that :— 



The Commission will only deal with propositions 

 that will introduce no change in the decisions arrived at 

 at previous congresses. 



A long discussion then took place as to whether it was 

 really necessary to give names to the C.G.S. units either 

 in the electrostatic or the electromagnetic systems, and 

 finally it was agreed to withdraw the proposition so far 

 as it dealt with the electrostatic system. 



The desirability of giving a name to the unit of 

 magnetic field and to the unit magnetic flux was strongly 

 urged, and as the names of Gauss and Weber had been 

 employed for some years in America for these units 

 respectively, the advantage of adopting these names for 

 the C.G.S. units of field and flux was advocated. On 

 the other hand, the resolution arrived at by the Electrical 

 Standards Committee of the British Association in 1895 

 to employ these names respectively for other units was 

 pointed out. Finally, the Commission, at the end of 

 their second sitting, on August 22, recommended the 

 following : — 



"The Commission is not of opinion that it is necessary 

 to give names to all the electromagnetic units. 



" However, in view of the use already of practical 

 instruments which give the strength of a magnetic field 

 directly in C.G.S. units, the Commission recommends 

 that the name Gauss be assigned to this unit in the 

 C.G.S. system. 



" The Commission proposes to assign to the unit of 

 magnetic flux, of which the magnitude will be subse- 

 quently defined, the name of Maxwell." 



These resolutions were brought before Section I. of 

 the Congress on August 24, and led to a long discussion. 

 M. Mascart opposed the giving a name to the C.G.S. 

 unit of magnetic field. The employment of practical 

 instruments for the direct measurement of the strength 

 of magnetic fields in C.G.S. units was not, in his opinion, 

 a sufficient reason for assigning a name to that unit. 

 Besides, this decision of the Commission appeared to be 



NO. 1609. VOL. 62] 



contrary to the spirit of the Congresses of 1881 and 1889, 

 which did not give the names of men to the C.G.S. 

 units. He admitted that the name of a man might be 

 given to the practical unit. In any case, the name of 

 "Gauss" seemed to him liable to give rise to confusion, 

 for Gauss was the originator of the first absolute system 

 employed, viz. that of the "millimetre-milligramme- 

 second " system, and that system, as distinguished from 

 the " centimetre, gramme, second " system, was still in 

 actual use in certain cases — for the measurement of the 

 earth's field, for example. 



Prof. Kohlrausch said that the "absolute units" were 

 enough for the physicists, but that, if the engineers felt 

 the need of practical units, Dr. Dorn and he did not 

 see that any inconvenience would arise from names being 

 given to them, such as those of Gauss and of Maxwell, 

 for example. The German delegates could not, how- 

 ever, commit their Government in the matter, and they 

 considered that the Congress should limit its recom- 

 mendations to the use of these new names without 

 seeking that legal sanction should be given to them. 



Prof Ayrtonagreed with M. Mascart, and mentioned that 

 during the past five years many " Ayrton-Mather Field 

 Testers " had been constructed to read off the strength 

 of a magnetic field directly in C.G.S. units, but that no 

 need for any special name for that unit had been felt in 

 connection therewith. He added, however, that, while 

 holding the opinion expressed by M. Mascart that it was 

 not desirable to give the names of persons to the C.G.S. 

 units, the units of field and flux had this peculiarity, that 

 without any multipliers they were the practical units 

 adopted. 



To this M. Mascart replied that the word " practical " 

 in this connection was ambiguous, since, although it was 

 true that the C.G.S. units of magnetic field and flux were 

 employed in practice, they did not belong to the so-called 

 "practical system." 



M. Hospitaller appealed to the Section to give names 

 to the unit of field and the unit of flux. He did not ask 

 for any legal decision in the matter, for the names 

 were put forward as a simple recommendation to the 

 Section. 



After a discussion in which Messrs. Ayrton, Carpentier, 

 Dorn, Hospitaller, Kohlrausch, Mailloux, Mascart, A. 

 Siemens, Silvanus Thompson and others took part, 

 Prof. Eric Gerard stated that in his opinion it was 

 desirable to come first to a decision that names should 

 be given to the C.G.S. units of magnetic field and to flux 

 of magnetic induction. 



M. Mascart, expressing his approbation of this idea, 

 the president of the Section, M. Violle, put the following 

 proposition formally to the meeting : — 



"The Section recommends the adoption of specific 

 names for the C.G.S. units of magnetic field and of 

 magnetic flux." This proposition being adopted, with 

 only two dissentients, the meeting was adjourned for a 

 short time to enable the members to exchange their views 

 regarding the exact names that should be employed. On 

 the meeting reassembling, the president put the two 

 following propositions successively : — 



(i) The Section recommends the adoption of the name of 

 Gauss yj?r the C.G.S. unit of magnetic field. 



(2) The Section recommends the adoption of the name of 

 MAXWELL/<7r the C.G.S. unit of magnetic flux , 



both of which were adopted with only two dissentients. 



On the same afternoon these resolutions of Section I. 

 were submitted to the Chamber of Government Delegates 

 to the Congress and adopted, and finally, at the closing 

 meeting of the Congress on Saturday, August 25, the 

 action which had been taken in the matter was formally 

 reported by M. Paul Janet, one of the two secretaries of 

 the Congress. 



