262 ROSA AND WOLFF: INTERNATIONAL ELECTRICAL UNITS 



tries, the mean of the values of the units realized at the Physi- 

 kalisch-Technische Reichsanstalt and National Physical Lab- 

 oratory. Altho the international ohm, as defined by the Lon- 

 don Conference, has not been strictly realized, the committee 

 believed that its value has been obtained in two independent 

 laboratories, with a good degree of precision, and that future 

 work will not change its value by more than 2 or 3 parts in 100,000. 

 The committee expressed the hope that new international 

 ohms, fulfilling all the specifications of the London Conference, 

 might be realized as soon as possible in different laboratories. 



2. STANDARD CELL COMPARISONS 



Each of the delegates brought with him a considerable number 

 of cells, which were repeatedly compared, under the most favor- 

 able conditions, with those of the Bureau of Standards, thus 

 furnishing a basis for expressing the results of the voltameter 

 work undertaken at Washington, as well as for further work in 

 the home laboratories. In addition, this made possible the 

 direct comparison of the standards of electromotivef orce employed 

 in the four institutions, and furnished data of value on the accu- 

 racy attainable in the reproduction of the Weston Normal Cell. 

 Further data on the last question were obtained from 48 cells set 

 up in Washington, with four samples of mercurous sulphate repre- 

 senting the methods of preparation adopted in the four insti- 

 tutions. Portions of each sample were washed according to the 

 procedure followed in the four laboratories, and three cells were 

 set up with each washed sample. In addition, two cells were 

 set up with each of four samples of cadmium sulphate submitted ; 

 comparative tests were also made of four samples of mercury and 

 of cadmium or cadmium amalgam. 



The comparisons were made in a basement room especially 

 fitted up for such work, in automatically controlled petroleum 

 baths, each of which was provided with coils for electric heating, 

 a cooling coil for water circulation when operating at tempera- 

 tures below that of the room, an efficient stirrer and means for 

 directing the circulation in the bath, and a sensitive thermo- 

 regulator, in addition to a rack for mounting the cells. 



