14 Mr. G. F. Rod well on the Theory of Phlogiston. 



of in Section I.) were distinguished from each other. Francis 

 Bacon was one of the first to deny the elemental nature of fire ; 

 he asserts that it is " merely compounded of the conjunction of 

 light and heat in any substance"*, and he elsewhere defines 

 heat as a violent motion of the smallest particles of bodies, and 

 light as a product of heat. Telesius of Consenza asserted that 

 heat is the cause of motion, cold of rest, — and that these incorpo- 

 real principles act upon passive matter, and by their mutual 

 reaction produce all the phenomena of the universe. This theory 

 was adopted and somewhat extended by Campanella. Athana- 

 sius Kircher, in his Ars Magna Lucis et Umbra, affirms that ordi- 

 nary fire is air caused to glow by the vehement collision of bodies, 

 by the heat of which combustible matter is changed into flame f- 

 Descartes assumed that all matter originally consisted of 

 square particles, which at the Creation were furnished with two 

 kinds of motion, the one producing the revolution of each par- 

 ticle around its own centre, the other the revolution of groups 

 of particles around a common centre. During this revolution 

 the angles of the particles became abraded by collision, and 

 hence were produced three elements. The first ("materia 

 coelestis," " materia subtilis," or " materia primi elementi ") con- 

 sists of the fine dust produced by the abrasion of the angles, and 

 moves with greater velocity than the other elements. The second 

 ("globuli secundi elementi"), of which the atmosphere and every- 

 thing between the stars and the earth is constituted^ consists of 

 the spheres which are produced by the abrasion of the square 

 particles ; it moves with greater velocity than the particles of the 

 third element. The third (" particulm tertii elementi"), of which 

 the earth and all terrestrial bodies are formed, consists of parti- 

 cles which are neither square nor spherical, are partially rounded 

 by abrasion, but retain some of their angles J. Fire consists of 

 particles of the third element rapidly agitated circularly by the 

 materia coelestis §, which is in perpetual motion, and is the cause 

 of all the motion in the universe. Light is apparent without heat, 

 as in the case of phosphorescent bodies, when the materia coelestis 



* Novum Organum, lib. ii. aph. 20. 



t " Ignis igitur noster usualis nihil aliud est, quara aer ex vehementi 

 duorura corporura collisione accensus, cujus ardore combustibilis materiae 

 fomes arreptus in flammam abit " (lib. i. cap. 1). The order of the Vicar- 

 General of the Jesuits (to which sect Kircher belonged), directing the print- 

 ing of the Ars Magna Lucis et Umbra, is dated December 18, 1644 ; it was 

 therefore published nearly simultaneously with the Principia of Descartes. 



X Principia, pars quarta. 



§ This idea of a circular motion in connexion with fire seems to have pre- 

 vailed at a much earlier period. Thus Seneca says, " Ignis enim natura in 

 verticem surgit, et, si nihil ilium prohibit, ascendit." (Qucsst. Natur. lib. ii. 

 cap. 24.) Vide also Aristotle, Ilepi Ovpavov, lib. i. cap. 2. 



