930 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



service in running two long lines each, which give the following 

 results, viz. : Grove's battery, per cup per month, $1.09 ; Chromic 

 acid battery, per cup per month, 31|c. to 35c. ; Hill's battery, per 

 cup per month, 4c. to 5c. Now, Ave may concede that ten cups of 

 this battery are required to perform w^hat might be done with 

 four of either of the others ; we see that economy is greatly in 

 its favor, for then the monthly expense is not more than one-third 

 that of the chromic acid, nor more than one-eighth that of Grove's. 

 Such results seem almost incredible, and yet the following gives a 

 record still more favorable for Hill's battery : 



I erected a series of 120 cups, which we put in operation at the 

 Western Union Office in New York, on the 23d of November last, 

 on one printing wire and one Morse Avire to Boston. It has been 

 running''constantly to the present time. During the first month, 

 thirty pounds blue vitriol were supplied, and on the 23d instant 

 (four months), ninety pounds only had been consumed, of which 

 the equivalent of zinc is a])out 23^ pomids ; but the zinc need not 

 be taken into the account, for the precipitated copper, being pure, 

 will sell for enough to offset the cost of all material consumed 

 except the blue vitriol. The ninety pounds of blue vitriol, at 

 eleven cents per pound (the present cost by the quantity), is $9.90, 

 or $1.24 per line per month, or a very small fraction over two 

 cents per cup per month for the two lines. This record was kept 

 and can be verified at the AVestern Union Office. The current was 

 admitted to be constant, smooth and satisfactory. 



I have experimented much in ascertaining the interior resistance 

 of the various batteries. I do this directly by the method hereto- 

 fore described in my paper on the Anthiatometer; also, by equa- 

 tions. 



By 01ms' law, 



e e 



— = s, and = s' 



r r -j- '>'' 



In which e = electro motive force; r = interior resistance; r' = 

 exterior, inserted resistance; s = strength of current in circulation; 

 s' = strength when r' is inserted. 



By eliminating e and reducing the equation, we have 



r' s' 



s — s' 

 For simple battery of one cup or more, I use the quantity gal- 



