16 Mr. G. F. Rodvvell on the Theory of Phlogiston. 



Clerk Maxwell. Already heat and light have been resolved into 

 dynamic phenomena ; and it is to be hoped that before long the 

 indefinite term " imponderable fluid " will disappear from our 

 text-books. At a time when we appear to be progressing to- 

 wards a comprehensive dynamical system, I venture to assert 

 that the Principia of Descartes and the l Whole body of Carte- 

 sian Philosophy ' of Anthony le Grand, may be perused by phy- 

 sicists with advantage, especially those portions relating to the 

 inception, continuance, and transference of motion, and the 

 various modes of motion possible to particles of matter. There 

 is indeed some fanciful, and much imaginary matter in the 

 Principia, and many relics of a bygone mode of thought ; but 

 there is also lucidity, accuracy of expression, and well-sustained 

 reasoning. Let us in perusing it bear in mind that it emanated 

 from an advanced mathematician, an accurate thinker, and one 

 of the most philosophic intellects of all time. 



Lemery*, in his famous Cours de Chimie, published in 1675 

 (consequently between the appearance of Becher's Physica Sub- 

 terranea and StahPs Zymotechnia Fundament alis), seems to have 

 adopted some of the views of Descartes. He asserts that the 

 acid of nitre has a great number of " corpuscules ignees" locked 

 up in it, as may be seen by the heating produced when we add 

 it to spirit of wine. " But because," he continues, " there may 

 be some difficulty in conceiving what is meant by little igneous 

 particles (corpuscules ignees), I do understand by them a subtle 

 matter (une matiere subtile) which, having been thrown into a 

 very rapid motion, still retains the aptitude of moving with im- 

 petuosity, even when it is enclosed in grosser matters ; and when 

 it finds some bodies which by their texture or figure are apt to 

 be put into motion, it drives them about so strongly that, their 

 parts rubbing violently against each other, heat is thereby pro- 

 duced." Elsewhere he affirms that the particles of sulphurs are 

 very susceptible of the motion j and he adds, " it seems probable 

 that fire is only a very violent motion of minute bodies round 

 their centre." 



Thus far we have observed no attempt to construct a compre- 

 hensive theory of combustion. This was first effected by Robert 

 Hooke ; and how admirably he succeeded, is,, I think, evident 

 from the passages quoted below. The theory was published in 

 1665, in Hooke's Micrographia, in a chapter "On charcoal or 

 burnt vegetables ; " and to the fact that it is buried in a mass of 

 irrelevant matter, that it occurs in a work in which one would not 

 expect to find a theory of combustion, and that there is nothing 

 to indicate its position, is probably to be traced the chief cause 

 of its neglect ; for in no age has it been well recognized, and 

 * Born 1645, died 1715. 



