concerned in the Phenomena of ordinary Electricity, §c. 207 



the wire from the conductor ; when very close, the deflection was 

 20°, and that was the maximum. When a Nairne's cylinder 

 machine was substituted, the deflection amounted to 85°; but 

 to effect this, it was necessary to give the cylinder three revolu- 

 tions in a second*. 



On these experiments, and some others of the same kind that 

 will hereafter be noticed, an argument in favour of the identity 

 of the agent in all electrical phenomena has been founded, and 

 apparently a very strong one. There are some points of view, 

 however, under which the evidence afforded by them is very 

 much weakened ; the following will show in what manner. 



I insulated a galvanometer of exceeding sensibility, and con- 

 nected its binding screws, by means of stout copper rods, with 

 the two conductors of a cylinder machine, which was capable of 

 giving twelve-inch sparks, and which, while in action, caused a 

 divergence in a gold-leaf electrometer (not connected with the 

 machine, and placed four yards distance) to such a degree that 

 the leaves often struck the pallets. On causing the cylinder to 

 revolve, sometimes very slowly, sometimes very rapidly, the gal- 

 vanometer remained undisturbed ; not the least symptom of de- 

 flection could be obtained. 



The astatic needle of this galvanometer weighed but 4 grs. 



The cause of the want of correspondence between this result 

 and that of M. Colladon is obvious. He employed a peculiar 

 galvanometer, so insulated as to prevent lateral communication 

 of electricity from layer to layer ; for unless his coil were, by 

 better insulation, in a condition to confine and sustain a charge 

 or current of common electricity at a higher intensity than such 

 coils ordinarily are, there would be no deflection. The high in- 

 tensity of electricity, caused by the interposition of a Leyden 

 battery, greatly promoted the effect ; and when the conductors 

 alone of a Nairne's machine were used, he found it necessary to 

 give intensity by a most rapid rate of revolution to the cylinder, 

 no less than three turns per second. 



In my experiment, the galvanometer coil, being only covered 

 with single silk, and having no oiled silk interposed between the 

 layers, was incapable of sustaining a high intensity, and there- 

 fore it failed to produce deflection even in the slightest degree. 

 But from this failure (an intentional one) important conse- 

 quences result, as will be seen from the following comparative 

 experiments. 



A \oltaic pair of elements was prepared, consisting of a copper 



r ^ irc tIu 11 ' ,,l ' il " ii'f'b in diameter and a thicker platinum wire. 



Tin-, wires, being properly connected with a galvanometer, were 



plunged to the depth of one-twelfth of an inch into concentrated 



* Annates de Ckimie et it P/iysiijne. xxxiii. fi:.'. 



