NOMOS. 17 



order, each revolution of the plate gave 10 or 12 

 sparks from the conductor, each an inch in length ; 

 and sparks of 10 or 14 inches in length could be 

 easily obtained. The electric battery used consisted 

 of 15 jars, each 23 inches in circumference, and each 

 having about 130 square inches of coating. The 

 galvanometer was one of ordinary sensitiveness, 

 having an arbitrary scale, of which each division was 

 equal to about 4. The discharging train was a thick 

 wire, the further extremity of which was connected 

 with the gas and water pipes belonging to the house. 

 The experiment was to charge the battery by thirty 

 turns of the machine, and then, having included a thick 

 wet string about ten inches in length in the circuit, 

 to discharge the battery through the galvanometer, 

 and notice the deflection of the needle. The result 

 was, that the needle immediately became deflected 

 through five and a half divisions of the arbitrary 

 scale. This is the first fact in the comparison. 



The next thing was to ascertain how much voltaic 

 electricity was required to produce this amount of 

 deflection ; and now the difficulty was to get a vol- 

 taic apparatus of sufficient minuteness. After many 

 trials, however, Dr. Faraday succeeded in finding 

 that the same degree of deflection was caused by 

 two mere wires, one of platinum and the other of 

 zinc, |^ths of an inch in length, T ^th of an inch in 

 diameter, and T %ths of an inch apart, when immersed 

 in four ounces of water acidulated with one drop of 

 ordinary sulphuric acid (a dilution of which the acid 

 could neither be tasted or tested with any distinct- 

 ness) for three seconds. 



c 



