208 Mr. M. Donovan on the supposed Identity of the Agent 



nitric acid. The needle whirled round the whole circle three 

 times. The immersed portion of copper wire weighed r ~ ^nd of 

 a grain, and no sensible portion of it was dissolved during 

 the momentary action. 



I coated a piece of the same wire with sealing-wax; and 

 having cut off a piece so that a fair section of the wire was pre- 

 sented, the wire was connected with the galvanometer, as also a 

 small platinum wire. The two wires were now immersed in a 

 few drops of nitric acid ; the needle started off 60°. This took 

 place in an instant of time, before Toff o o^th of a grain of metal 

 could have been dissolved. The surface of copper exposed in 

 this case was a circular disc jxyth of an inch in diameter. 



A still more remarkable case is the following : — A voltaic 

 combination was made of two platinum wires, to the end of one 

 of which was affixed a bit of gold-leaf weighing by calculation 

 about 6' 1 00 dtfa of a grain. This combination, when brought in 

 contact with a single drop of nitromuriatic acid, caused the needle 

 to start off 160°; not more than half of the gold appeared to be 

 acted on by the acid. 



Here then the most feeble voltaic electricity that could be 

 produced was found highly active in causing deflection, although, 

 of common electricity, neither the highest nor the lowest in- 

 tensity had the slightest effect. The defence that the supporters 

 of identity would offer against the evidence of these comparative 

 experiments would be, that the quantity of voltaic electricity, 

 although feeble in intensity, is immeasurably greater, in the case 

 of the minute particles of metals above described, than any cur- 

 rent which the frictional electricity can supply. Such an ex- 

 planation may, in the present instance, be pronounced unsatis- 

 factory. On the contrary, the quantity of common electricity 

 in my experiment must have been far greater, because the gal- 

 vanometer coil was charged with its highest endurable intensity ; 

 and so much so, according to Colladon's explanation, as to cause 

 a lateral overflow, although the excess must have left the wire 

 charged as fully as its single insulation could sustain. So high 

 an intensity could not have subsisted in the coil unless the quan- 

 tity of electricity were very much greater than the coil could 

 transmit, for intensity is the ratio of quantity to space. Yet it 

 is remarkable that the same coil readily transmitted, and endured 

 without lateral escape, all the voltaic electricity which the minute 

 particles of zinc and platinum had evolved. 



Some persons draw a distinction between statical and current 

 electricity, which they deem all-sufficient in explaining differ- 

 ences of effects such as the foregoing. Now a current has never 

 been proved to run in voltaic phenomena in any other manner 

 than it does when a stream of electricity passes from the positive 



