154 ANNUAL OF SCIENTIFIC DISCOVERY. 



of our Grove cell upon the water is the equivalent of 1.105 X 772 =. 

 81 (call it 80) foot-pounds per minute. 



It is well known that a galvanic battery will perform its maxi- 

 mum work when the external resistance which it encounters is 

 equal to the internal resistance of the battery. I have found the 

 internal resistance of the pint-cup Grove cell to be equal, on the 

 average, to that of 100 feet of pure copper wire, No. 18 size. 

 Hence the maximum external effect of the ordinary Grove cell 

 may be set down as the equivalent of 80 foot-pounds per minute, 

 equal to the production of 80 -J- 15 =. 5| candle lights. I would not 

 be understood as saying that this amount of light can be produced 

 by a single Grove cell, but that 1,000 cells, if properly arranged, 

 would be capable of evolving somewhat more than 5,000 caudle 

 lights from a single lamp. 



With sulphuric acid costing 2k cents, nitric acid 10 cents, zinc 8 

 cents, and mercury 50 cents per pound, the cost of running 1,000 

 Grove cells 1 hour, while doing their maximum work, would be 

 27.65. This would give for 5,000 candles a cost of about 5i 

 mills per hour per candle. 



The cost of gas light per candle per hour would be about 1 

 mill, if gas costs 3.25 per thousand cubic feet, and if 1 cubic 

 foot per hour gives the light of 3 candles. 



With the Smee battery, carefully managed, the cost of 5,000 

 candle lights would be about the same as with gas. 



Let us now look at the cost of electricity as developed by the 

 magneto-electric machine. The power expended on the machine 

 is consumed in friction, in heating the wires, magnets, etc. On a 

 well-built machine which I examined in 1861, 1,100 foot-pounds 

 per minute were required to keep the machine in mot' . when the 

 circuit was open, and the machine doing no work. Lut when the 

 circuit was closed, 3,200 foot-pounds per minute were required to 

 maintain the same velocit} 7 of rotation ; nearly all this excess of 

 power (namely, 2,100 foot-pounds) was measured as electricity, 

 about two-thirds (say 1,300 foot-pounds) being expended inter- 

 nalh', heating the coils and magnets, etc., and the balance, 800 

 foot-pounds, measured as external useful effect. Had the exter- 

 nal resistance been larger, a greater proportion of the expended 

 power would have appeared as useful effect. Suppose, however, 

 that only 800 foot-pounds per minute could be utilized by this 

 machine and used for illuminating purposes. This would be the 

 equivalent of 800 -f- 15=53.33 candles, and the to f i! power re- 

 quired (including friction, etc.) would be 3, 200 -^-53. 3o = 00, about 

 GO foot-pounds per minute per candle. 



In the vicinity of Boston, power is furnished, per horse-power, 

 at the rate of 180 per year of 313 days of 10 hours each, or at 



ISO 

 the rate of- -=$0.0575 (5| cents) per hour. If only one- 



01.1 vx -I f\ \ ^ / f v 



33.000 _ 



fourth of this power could be utilized as light, - - 550 candles 



4X 15 



would be the equivalent of 1 horse-power, and would cost 



