312 Royal Institution. 



tive philosophy, viz. the period of the alchemists, we find many na- 

 tural phenomena referred to spiritual causes. Paracelsus taught 

 that the Archa?us or stomach demon presided over, caused and regu- 

 lated the functions of digestion, assimilation, &c. 



Van Helmont, who may he considered in many respects the turn- 

 ing-point between alchemy and true chemistry, adopted with some 

 modification the Archseus of Paracelsus and many of the opinions of 

 the Spiritualists, hut showed tendencies of a more correctly inductive 

 character ; the term ' Gas,' which he introduced, gives evidence of 

 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 che- 

 mical system. 



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

 his discovery of the weight of air was mainly instrumental in 

 changing the character of thought and inducing philosophers to 

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

 which affected 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 ana- 

 logous 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 aether. Sound is now admitted to be an 

 undulation 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. Rumford 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, 

 showed that what had hitherto been deemed stumbling-blocks 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 pre- 

 sent 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 hypothesis of a fluid is not considered necessary for the latter ; 

 and need not be so for the former class of phenomena. 



