636 



Mr. H. E. Schmitz on the 



Y 4 Z 4 ; the battery current is never interrupted except at the 

 moment of commutation. 



Let the first system of connexions produce a current i 

 through the compensation circuit BB'A. The second system 

 of connexions either produces no current through the circuit 

 BB'A, or, by joining Y 1 Z l3 Y 2 Z 2 as well as Y 3 Z 3 and Y 4 Z 4 , 



produces a current approximately -— . 



Meanwhile the battery is producing a current through 

 a resistance which never differs much from 10,000 ohms. 

 The larger current is used when the standard cells are to 



Standard cells 

 Thermo -el em en t 



' a: 



y* 



Fig. 2. 





3 '3*-3 



&0k£4 



D/WtELL 



Battery 



be balanced, the smaller when the thermo-element is to be 

 balanced. 



It was undesirable to make the commutation at frequent 

 intervals, and it was therefore of special importance to be 

 able to assume constancy of the auxiliary battery during 

 periods of an hour or two. Accumulators were tried under 

 various conditions, but the rate of fall of electromotive force 

 was in all cases too great. Finally, four large Daniell cells, 

 each containing two litres of saturated copper-sulphate solu- 

 tion and about one-tenth that volume of zinc-sulphate solution 

 of density 1*2, were employed. These could be trusted to 

 give a nearly constant current for several weeks together, the 

 variation during the course of a day being as a rule exceedingly 

 small. In this connection the following record may be of 

 interest : — 



