432 POPULAR LECTURES AND ADDRESSES. 



On the other hand, the dynamical energy of 

 luminiferous vibrations was referred to as the 

 mechanical power allotted to plants (not mush- 

 rooms or funguses, which can grow in the dark, 

 arc nourished by organic food like animals, and 

 like animals absorb oxygen and exhale carbonic 

 acid), to enable them to draw carbon from 

 carbonic acid, and hydrogen from water. 



In conclusion, the sources available to man for 

 the production of mechanical effect were examined 

 and traced to the sun's heat and the rotation of 

 the earth round its axis. 



Published speculations 1 were referred to, by 

 which it is shown to be possible that the motions 

 of the earth and of the heavenly bodies, and the 

 heat of the sun, may all be due to gravitation ; or 

 that the potential energy of gravitation may be in 

 reality the ultimate created antecedent of all motion, 

 heal, and light at present existing in the universe^ 



1 Ti;tns. Roy. .SVv. Edinburgh, April, 1854 ^Professor \V. 

 Thomson, "On the Mechanical Energies of the Solar System. 

 Als., Jiritish .Issa-infion Report, Liverpool, September, 1854 

 "On the Mechanic d A nlccrdents of Motion, Heat, and Light." 

 Kepulilished in Vol. II. of Mathematical and Physical Pa; 



