4 HYPOTHESIS OF NEWTON. 



theory ; and that, in reality, they had no fixed or 

 settled opinions on the subject. 



The authority of Sir Isaac Newton has been 

 often cited in support of the doctrine, that caloric 

 is not a material substance. But it is worthy of 

 special notice, that in all the latest works of that 

 great man on physical science, he maintains the 

 existence of what he calls " an exceedingly sub- 

 tile and elastic ethereal substance, which is dif- 

 fused through all places, fills the pores of gross 

 bodies, and forms a large constituent of their 

 bulk or volume." In a letter addressed to the 

 celebrated Boyle in 1678, the object of which 

 was to explain his views of the aether, he repre- 

 sents it as " the cause of cohesion, capillary attrac- 

 tion, and of the force by which menstruums per- 

 vade and dissolve solid bodies." He adds in another 

 sentence, " I conceive the atmosphere to be com- 

 posed of the particles of all sorts of bodies of which 

 the earth consists, separated and kept at a distance 

 from one another by the same active principle"* 



* The above views were still further expanded in a scholium 

 at the close of the second edition of the Principia, published in 

 1713; and in the form of queries, they were reiterated at the 

 close of the Optics, published in 1717. In both of these great 

 works, he represents the sether as the cause of gravity, cohesion, 

 capillary attraction, solution, elasticity, the emission, reflexion, 

 refraction, and inflexion of light. He also maintained that the 

 sether is the cause of animal motion. Yet he observes, that he 

 knows not what the aether is; and that " we have not that suf- 

 ficiency of experiments which are requisite to an accurate deter- 

 mination of the laws by which this subtile spirit operates." 



