492 vETHER OF NEWTON. 



that animal heat was produced by the motion of 

 the blood, and friction of different parts of the 

 body, because the temperature of animals is in- 

 creased by motion and exercise. 



The cether of Sir Isaac Newton, to which, in 

 various parts of his later writings, he referred 

 gravitation, cohesion, capillary attraction, the 

 emission, reflexion, refraction, and inflexion of 

 light, the elastic force of gaseous bodies, and the 

 power of menstruums to dissolve solids, was 

 identical with the Ai0ep of Orpheus, and the an- 

 cient sages of the East. He further suggests, in 

 the Third Book of Optics, that " animal motion 

 may be performed by the vibrations of this asther, 

 excited in the brain by the power of the will, 

 and propagated thence through the capillaments 

 of the nerves into the muscles, for contracting 

 and dilating them." 



It is therefore evident that Newton did not 

 always regard attraction and repulsion as ulti- 

 mate phenomena, but that he referred all the 

 operations of nature, including animal motion, to 

 what he termed an " unknown aether," which I 

 have shewn to be identical with caloric. Yet so 

 imperfect were the views of this great mathema- 

 tician in regard to the nature of heat, that he re- 

 presents it as an effect of vibrations of the aether. 

 Had he been aware that the velocity of the pla- 

 nets through their orbits is directly in propor- 

 tion to the heating power of the sun, which 



