120 NOTICES OF THE MEETINGS [Feb. 13, 
Passing to the period antecedent to the time of more strict 
inductive philosophy, viz. the period of the Alchemists, we find many 
natural phenomena referred to spiritual causes. Paracelsus taught 
that the Archzus or stomach demon presided over, caused, and 
regulated the functions of digestion, assimilation, &c. 
Van Helmont, who may be considered in many respects the turning 
point between Alchemy and true chemistry, adopted with some 
modification the Archzeus of Paracelsus and many of the opinions of 
the Spiritualists, but shewed 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 classifying 
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 
changing 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 
analogous 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 
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 
doctrine 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 
explained 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 hypothesis of a fluid is not considered necessary for the latter, 
and need not be so for the former class of phenomena. 
