344 Sir W. Snow Harris on a General Law of 



one over the other, or otherwise wires of various lengths intro- 

 duced, by fixing them either straight or curved between the two 

 upper holes, or by placing them diagonally between the \ipper 

 and under holes, — a practice pursued by some of the continental 

 philosophers, and indicated and figured by M. Pouillet in his 

 work, Elemeiis de Physique. 



6. Having thus, for the sake of clearness, described and ex- 

 plained my instrument, such as it was when first invented and 

 afterwards perfected, it may not be unimportant to quote some 

 sti-iking instances of its practical application. It has been well ob- 

 served by the justly celebrated English chemist. Sir H. Davy, that 

 "nothing is more important to the progress of science than the 

 invention and application of a new instrument," that " the intel- 

 lectual faculty is not more the source of success in physical dis- 

 covery than the nature of the means which we are led to employ*." 

 In the first place, however, I may observe that there is really no 

 well-established law of electricity with which the indications of 

 my instrument are not in perfect accordance, the results arrived 

 at by M. Kiess not excepted, as I shall presently show. This 

 understood, it is to be further observed, that it was through the 

 agency of this instrument, fig. 5, that Faraday first observed the 

 heating powers of the magneto-electric current during the meet- 

 ing of the British Association at Oxford in 1832t. The heating 

 effect of the shock of the Gymnotus was first observed with this 

 instrument at the Adelaide Gallery in London, in 1839, by Mr. 

 Gassiot and myself. In the course of our experiments we em- 

 ployed a fine silver wire turned into a helix, as first suggested 

 by Mr. Gassiot. Dr. Dav}^, F.R.S., describes in his most inter- 

 esting work, entitled ' Physical and Anatomical Researches,' 

 the great success of my instrument in rendering sensible the 

 heating effects of the shock of the torpedo : he says, " the sen- 

 sibility of this instrument is so great, that the spirit in the stem 

 was not only moved by a single spark from the electrical machine, 

 but even very distinctly by the electricity of a single voltaic 

 combination composed of copper and zinc wire ; the former ■^ji\\ 

 of an inch in diameter, the latter jyth, excited by dilute sul- 

 phuric acid." This instrument, he further observes, "was 

 strongly affected by active fish, and even distinctly by weak 

 ones ; indeed, occasionally, when it formed part of a circle in 

 connexion with the galvanometer, I have seen it affected alone, 

 the galvanometer affording no indication." Dr. Davy, in his 

 experiments, em])loyed an exceedingly fine wii'e of platinum, 

 drawn down by Wollaston's method, described in the Philosophical 

 Transactions for 1813; he employed also a stopcock for regu- 



* " Elements of Chemistry." 



t Faraday's Experimental Researches, 3rd series, p. 98. 



