March 2, 1883.] 



SCIENCE. 



87 



FRIDAY, MARCH 2, 1883. 



THE INTERNATIONAL CONFERENCE 

 FOR THE DETERMINATION OF THE 

 ELECTRICAL UNITS. 



At a meeting of the electrical congress, Oct. 

 5, 1881, it was recommended that the French 

 government should invite the other powers to 

 constitute an international commission to dis- 

 cuss the following points : — 



1. To determine for practical science the 

 conditions which a column of mercurj^ should 

 fulfil in order to represent the electrical unit of 

 resistance. 



2. To determine upon a definite standard of 

 light. 



3. To arrange a systematic and universal 

 plan for studying atmospheric electricity, ter- 

 restrial magnetism, and the exchange of in- 

 ternational observations. 



In accordance withthis recommendation the 

 French government communicated with the 

 other powers ; and representatives appointed 

 by the various governments assembled iu Paris, 

 Oct. 16, 1882, at the residence of the foreign 

 minister. At the first meeting there were 

 forty -seven representatives present, among 

 whom were Helmholtz, W. Siemens, Wiede- 

 mann, Kohlrausch, Frohlich, Lorenz, Dumas, 

 Mascart, Tacchini, and Weber. The repre- 

 sentatives from Great Britain and the United 

 States had not been notified in time to attend 

 the opening of the conference. 



Upon organization, three committees were 

 formed, — one upon electrical units, one upon 

 earth-currents and lightning-rods, and another 

 upon a standard of hght. At first the time 

 of the conference was largely devoted to dis- 

 cussions of the best methods of determining 

 the unit of electrical resistance. Various sug- 

 gestions were made in regard to the limits of 

 accuracy, and to the necessity of repeating 

 the observations already made at different 

 places on the earth's surface, in order to elim- 

 inate the errors due to locality. M. Broch 

 of Norway suggested that the calorimetric 

 determinations of the ohm should be care- 

 fully made ; this method being the most direct 

 one, although it required a precise value of 



No. 4.— 1883. 



the mechanical equivalent of heat. Sir W. 

 Thomson and Helmholtz pointed out that the 

 heat method depended upon the measurement 

 of current, and could only be considered as 

 a method of control. MM. Lorenz and Roiti 

 presented papers upon the determination of 

 the ohm, and Wiedemann gave a bibliography 

 of the subject. After hearing the careful and 

 minute discussion of the subject, the following 

 resolutions were adopted : — 



1 . The commission consider that the deter- 

 minations made up to the present time are not 

 sufficiently concordant to allow the value of 

 the ohm to be fixed. 



They believe that it is necessary to continue 

 the researches upon this value. Although they 

 do not advise observers to restrict themselves 

 in the choice of methods, thej- consider the fol- 

 lowing methods particularly adapted for exact 

 determinations : — 



a. Induction of a current upon a closed cir- 

 cuit (Kirchoff). 



6. Induction by the earth (W. Weber). 



c. Decrement of moving magnets (W. 

 Weber) . 



d. Apparatus of the British association. 



e. Methods of M. Lorenz. 



It is also desirable to determine the ohm by 

 the quantity of heat evolved by a given cur- 

 rent, using this method as a control method. 



2. It is thought desirable that the French 

 government should take the necessary steps to 

 prepare certain standards of resistance, which 

 can be placed at the disposal of scientific men, 

 in order to compare their values. 



The commission was, at first, of the opinion, 

 that when the results of the different observers 

 reach an approximation of xoVff *^f ^^^ '^'^i® 

 value, the value of the iDractical unit of resist- 

 ance should then be fixed. After much dis- 

 cussion, it was felt that no decision upon the 

 limit of accuracj' could be reached at present. 

 Mascart then described the methods adopted 

 for the studj' of atmospheric electricity. Sir 

 W. Thomson showed that it was important to 

 make observations upon the air in a definite 

 enclosure, or, in other words, upon the air 

 itself. Helmholtz in this connection remarked, 



