102 CORRELATION OF PHYSICAL FORCES. 



vapour of some substance dissipated by the discharge ; on the 

 other hand, it seems more consonant with experience to re- 

 gard these effects as produced by force, as we have analogous 

 effects produced by admitted forces, in cases where no one 

 would invoke the aid of a hypothetic fluid for explanation. 

 For instance, glasses may be broken by electrical discharges ; 

 so may they by sonorous vibrations. Metals electrified or 

 magnetised will emit a sound ; so they will if struck, or if a 

 musical note with which they can vibrate in unison be sounded 

 near to them. 



Even chemical decomposition, in cases of feeble affinity, 

 may be produced by purely mechanical effects. A number of 

 instances of this have been collected by M. Becquerel ; and 

 substances whose constituents are held together by feeble af- 

 finities, such as iodide of nitrogen and similar compounds, are 

 decomposed by the vibration occasioned by sound. 



If, instead of being regarded as a fluid or imponderable 

 matter sui generis, electricity be regarded as the motion of an 

 ether, equal difficulties are encountered. Assuming ether to 

 pervade the pores of all bodies, is the ether a conductor or 

 non-conductor ? If the latter that is, if the ether be incapa- 

 ble of transmitting the electrical wave the ethereal hypothe- 

 sis of electricity necessarily falls ; but if the motion of the 

 ether constitute what we call conduction of electricity, then 

 the more porous bodies, or those most permeable by the 

 ether, should be the best conductors. But this is not the case. 

 If, again, the metal and the air surrounding it are both per- 

 vaded by ether, why should the electrical wave affect the 

 ether in the metal, and not stir that in the gas ? To support 

 an ethereal hypothesis of electricity, many additional and 

 hardly reconcilable hypotheses must be imported. 



The fracture and comminution of a non-conducting body, 

 the fusion or dispersion of a metallic wire by the electrical 

 discharge, are effects equally difficult to conceive upon the 

 hypothesis of an ethereal vibration, as upon that of a fluid, 



