284- Mr. Gassiot on an Experiment exhibitmg 



preconceived notion we might have entertained of the results 

 of any disturbance in that equilibrium ; we must, therefore, for 

 the present content ourselves with adiTfitting that some un- 

 known cause exists, which upon the contact of zinc and cop- 

 per determines the transfer of the positive and negative elec- 

 tricities respectively to the two surfaces which are brought in 

 apposition." 



Early in 1843 Professor Grove devised an experiment, a de- 

 scription of which appears in the reports of a lecture given by 

 that gentleman at theLondon Institution, on the 18th of January 

 of that year : the experiment is thus described in the Literary 

 Gazette of the 21st of the same month : — " Discs of zinc and 

 copper were juxtaposed surface to surface, contact being pre- 

 vented by a rim of paper, and yet when separated the electro- 

 scope was affected : here then was no contact, and yet the elec- 

 trical effects were produced, which should be so by the mutual 

 radiation, but which could not be by the contact theory." 



Mr. Grove thinks the electrical phaenomena due to a radia- 

 tion similar to that which takes place in the experiments of 

 Moser and others, and which produces a change, either phy- 

 sical or chemical, upon the surfaces of the plates. 



On the 10th of February in the same year Mr. Grove re- 

 peated the experiment at the Royal Institution (Electrical 

 Magazine, vol. i. p. 57), but still by many it has not been 

 considered an unexceptionable experiment ; and, considering 

 its important bearing on the contact theory, the objections 

 that have been raised are certainly deserving of attention : by 

 some, it has been inferred that the mere interposition of a rim 

 of paper might not have prevented actual metallic contact in 

 the portions of the discs which were not similarly protected ; 

 by others, it is somewhat fairly assumed that a certain amount 

 of friction must be produced by the pressure of the discs 

 against the paper, and that this would in itself be sufficient to 

 account for the very slight signs of tension which were deve- 

 loped, although this objection would equally apply to the ex- 

 periment of Volta. 



It appears to me rather extraordinary, considering the im- 

 portance of the experiment, that no further attempts have been 

 made to render it unexceptionable. 



In the Phil. Trans, for this year * I have described an elec- 

 troscope by means of which the tension in a single pair of the 

 voltaic battery is rendered distinctly appreciable. Since its 

 publication it Jias occurred to me, that by means of this in- 

 strument I could repeat Mr. Grove's experiment without the 

 objectionable points to which I have alluded, and after a few 

 * See the following paper. — Edit. 



