On a new Modification of the Bichromate Battery. 201 



temperature : we here see an explanation of how thunder-clouds 

 may be formed. It is probable, however, that in the ordinary 

 phenomena of atmospheric electricity and earth-currents the 

 real charges possessed by portions of the atmosphere may have 

 but little effect ; but on this point we cannot at present express 

 a decided opinion. 



We beg to remain, Gentlemen, 



Very truly yours, 



John Perry, 

 W. E. Ayrton. 



XXVIII. On a new Modification of the Bichromate Battery. 

 By H. C. Russell*. 



[Plate VIII. fig. 14] 



Sydney Observatory, 

 My dear Sir, May 31, 1877. 



YOU were kind enough to advise me, when I was in 

 England, about the purchase of a large Ruhmkorff coil. 

 In using it, I have had the ordinary bichromate-of-potash cells 

 to develop the electricity, and of course have had to suffer the 

 inconveniences which attend the use of a cell which falls off so 

 quickly. This has induced me to look for a more constant form 

 of electric generator ; and I have found one that is perfectly 

 constant in its action, and will remain so as long as the solution 

 and zinc are supplied. I enclose a section-drawing (PI. VIII. 

 fig. 14); and you will see I have adopted a modification of one 

 of Darnell's earliest ideas for obtaining a constant current. The 

 solution used is the ordinary bichromate of potash, in the 

 arrangement shown, which perhaps needs little explanation ; 

 but I may say that a drop of solution per second keeps the cell 

 in full and steady work. The drawing is at fault in one 

 respect ; the only space in the cell for solution is between the 

 plates, not, as shown, all round the plates : the object of this is 

 to make all the solution pass the face of the zinc. You will 

 observe that, supposing the waste-tap shut and the drop- 

 tap above opened, the solution accumulates in the cell till 

 it comes to the level of the overflow-pipe; and then, for every 

 drop which goes in, one goes out ; but as the overflow-pipe 

 begins at the bottom of the solution, it is the used or waste 

 solution which must go out. When the battery is not required, 

 the waste-tap is opened and the other shut, and the battery- 

 cell is left perfectly inactive and ready for the next time it 

 is wanted. There is of course some additional first cost ; but 



* Communicated by Dr. Huggins, F.E.S. 



