concerned in the Phenomena of ordinary Electricity, S$c. 343 



deflection ; and that a little electricity, or one hundred times 

 more, may produce equal deflection, provided that both quantities 

 are constrained to pass through the galvanometer at the same 

 degree of intensity. The intensity of the small quantity may 

 endure for a much shorter time than that of the large quantity ; 

 but the effect on the needle once produced, it will not, during 

 its swing, give any indication of the length of time (in cases of 

 such momentary passage as that from a Leyden battery) during 

 which the effort was sustained in the coil ; the momentum of 

 the needle will determine the rest. 



The law already laid down was inferred by Faraday from his 

 experiment of passing common electricity through a galvano- 

 meter under various circumstances. He states, that "the next 

 point was to obtain a voltaic arrangement producing an effect 

 equal to that just described" with common electricity. A wire 

 of platinum and a wire of zinc, each being one-eighteenth of an 

 inch in diameter, were properly connected with the galvano- 

 meter. Their other ends were plunged five-eighths of an inch 

 deej) in a mixture of one drop of strong sulphuric acid in four 

 ounces of water, and w r erc retained there for T f ^thsof a minute, 

 after which they were quickly withdrawn. The galvanometer 

 needle was deflected to 22°, exactly as in the case of the previous 

 experiment with common electricity. From this experiment 

 with the wires, assisted by the law already referred to, he drew 

 as a conclusion, that the electricity evolved during T fo tns 0I " a 

 minute, by a zinc wire and a platinum wire, each one-eighteenth 

 of an inch diameter, immersed to the depth of five-eighths of an 

 inch in four ounces of water containing one drop of sulphuric 

 acid, is equal to the electricity produced by a Leyden battery 

 charged by thirty turns of a powerful plate-machine which gave 

 ten or twelve sparks an inch long each turn, from a brass con- 

 ductor exposing 1422 square inches of surface. That is, a wire 

 which presented one-ninth of a square inch in surface, afforded 

 in yfyths of a minute, electricity equal to 300 or 360 dense 

 sparks taken from 1422 square inches (almost ten square feet) 

 of a prime conductor. Hence, according to the above-mentioned 

 law, he inferred the equality of the two " absolute quantities " 

 of electricity from the fact, that the galvanometer needle suffered 

 equal deflection from both quantities (371.). 



The purpose of this experiment was still further to support 

 tlic inferred identity of voltaic and iVictional electricity, by redu- 

 oing thnii under obedience to one common law ; and next, to 

 establish tin- estimate, already alluded to, of the enormous quan- 

 tity of electricitj with which matter is naturally associated. It 

 is t>< be inquired how far the experiment supports either of these 

 positions, although the considerations already adduced appear to 

 "ii' ( i sufficient objections without further arguments. 



