APPENDIX TO PAGE 18. 



Development of Knowledge of Heat from 1650. — 

 Hooke' s Vibratory Theory of Heat and Light. — Heat as 

 a measurable Fluid. — Heat as an indestructible Fluid. — 

 "Caloric" ; invented by Lavoisier. — Extracts from "Micro- 

 graphia" by Hooke. — Extracts from " Traite Elementaire 

 de Chimie? by Lavoisier. 



The following extracts from the Micrographia show 

 that, already in 1660, Robert Hooke had carried the 

 mechanical theory of heat out of the region of speculation,, 

 and adduced experimental proofs that heat and light have 

 their origin in the invisible vibratory motions of matter,, 

 and are communicated through space by the vibratory 

 motions of the ether ; and had given such definition to his 

 theory that he was thereby enabled to give the now accepted 

 explanations of fluidity and combustion, and to point to the 

 deflection of the wave fronts (" pulses in orbem ") when 

 waves pass obliquely from one medium into another in 

 which they move with a different velocity. 



The papers from which these extracts are taken were 

 read before the Royal Society between the years 1660 and 

 1664, when the "Micrographia" was published, and it is on 

 record (" Posthumous Works of Robert Hooke," by Richard 

 Wallis, 1705, p. 8) that these papers made Hooke much 

 respected by the Society. It appears that, for some time after 

 these views had been expressed, heat was very generally 



