DR. DAVY ON THE TORPEDO. 643 



on this subject, completely establishing- Mr. Faraday's anticipation. The instrument 

 employed was similar to that described by Mr. Harris in the Philosophical Trans- 

 actions of 1827, differing- merely in the wire passed through the small globe being 

 exceedingly fine, and of platina, formed after Dr. Wollaston's method*; in having a 

 small stop-cock for regulating the height of the spirit in the stem ; and in using as 

 small a quantity of spirit as possible -)-. The delicacy of this instrument was so great, 

 that the spirit was not only moved by a single spark of the electrical machine, but 

 even very distinctly by the electricity of a single voltaic combination, composed of a 

 copper and zinc wire, the former Vrth of an inch in diameter, the latter -^, excited 

 by dilute sulphuric acid. 



This instrument was strongly affected by active fish, and even distinctly by weak 

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

 galvanometer, I have seen it affected alone, the galvanometer affording no indication 

 of the passage of the electricity. Using two air thermometers of the same construc- 

 tion, each connected with the wires for contact at one end, and with a galvanometer 

 at the other, the heating effect of the electricity of the Torpedo has been apparently 

 diminished, and even more distinctly diminished on adding to the circle another link 

 of very fine platina wire. And at the same time its influence on the galvanometer has 

 been diminished, and its power of imparting permanent magnetism to a needle placed 

 in a spiral, both forming part of the circle. 



When heat has been applied to the extra link of platina by means of a spirit lamp, 

 so as to render it red hot, the diminution of effect has disappeared ; and equally so, 

 as well as I could judge from many experiments, whether acting on the thermometer, 

 the galvanometer, or the needle in the spiral. 



It appeared not improbable that a short portion of a very fine platina wire might 

 be ignited in the passage of the electricity of the Torpedo. I have made several ex- 

 periments to ascertain this, but have never witnessed the effect, even in perfect dark- 

 ness, and using fish, the discharge of whose electricity at the same time converted a 

 needle into a tolerably powerful magnet, the needle having been put into a spiral 

 connected with the fine wire, so as to afford a test of the strength of the electricity. 

 This want of ignition may at first view seem contrary to the effect on the thermo- 

 meter ; but perhaps it ought not to be considered so, taking into account the rapid 

 manner in which the heat evolved in the fine platina wire must be carried off by the 

 adjoining compound wire of platina and silver. 



The experiments detailed in my former paper were demonstrative that the elec- 

 tricity of the Torpedo is capable of acting like voltaic electricity in effecting chemical 



* Philosophical Transactions, 1813, p. 114. 



t I mention these circumstances because I have not been able to refer to Mr. Harris's later account of his 

 instrument, published in the Philosophical Transactions of the Royal Society of Edinburgh. I should add that 

 the bulb of the thermometer was defended from the variable temperature of the surrounding air by being in- 

 cluded in a wooden box. 



4 A 2 



