Heating Effects of Electricity and Magnetism. 63 



the thought involved in it by its derivation from ' Geist,' a ghost or 

 spirit. By regarding it as intermediate between spirit and matter, 

 by separating it from common air, and by distinguishing or classify- 

 ing different sorts of gas, he paved the way for a more accurate 

 chemical system. 



Shortly after the time of Van Helmont, lived Torricelli, who, by 

 his discovery of the weight of air, was mainly instrumental in chang- 

 ing the character of thought, and inducing philosophers to introduce, 

 or at all events to develope, the notion of fluids as agents which 

 effected the more mysterious phenomena of nature, such as light, 

 heat, electricity, and magnetism. 



Air being proved analogous in many of its characters to fluids as 

 previously known, the idea of fluids or of an ether was carried on to 

 other unknown agencies appearing to present effects remotely analo- 

 gous to air or gases. 



Sound was included by some in the same category with the other 

 affections of matter, and as late as the close of the last century, a 

 paper was written by Lamarck to prove that sound was propagated 

 by the undulations of an ether. Sound is now admitted to be an un- 

 dulation or motion of ordinary matter, and Mr Grove considered that 

 what have been called the imponderables, or imponderable fluids, 

 might be actions of a similar character, and might be viewed as 

 motions of ordinary matter. 



Heat was at an early period so viewed, and we find traces of this 

 in the writings of Lord Bacon. Rum ford and Davy gave the doc- 

 trine a greater development ; and Mr Grove, in a communication 

 made by him at an evening meeting of this Institution in 1847, 

 shewed that what had hitherto been deemed stumblingblocks in the 

 way of this theory of heat, viz., the phenomena presented by what 

 have been called latent and specific heat, might be more simply ex- 

 plained by the dynamic theory. 



In this evening's communication, he brought forward some experi- 

 ments and considerations in favour of the extension of this view to 

 electricity and magnetism, an extension which he had for many years 

 advocated, and which was, in his opinion, supported by many analogies. 



The ordinary attractions and repulsions of electrified bodies present 

 no more difficulties when regarded as being produced by a change in 

 the state or relations of the matter affected, than did the attraction 

 of the earth by the sun, or of a leaden ball by the earth ; the hypo- 

 thesis of a fluid is not considered necessary for the latter, and need 

 not be so for the former class of phenomena. 



In the cases of heating or ignition of a conjunctive wire or con- 

 ducting body through which what is called electricity is transmitted, 

 we have many evidences that the matter itself is affected, and in 

 some cases temporarily, in others, permanently changed ; thus if a 

 wire of lead is ignited to fusion by the voltaic battery, the fused lead 

 being kept in a channel to prevent its dispersion, it gradually shortens, 



