Antecedents of Motion, Heat, and Light. 93 



the particles of carbon and hydrogen away from those of oxy- 

 gen, towards which they are attracted with such powerful 

 affinities ; and that luminiferous motions are reduced to rest 

 to an extent exactly equivalent to the potential energy thus 

 called into being. Whether or not the coolness of green 

 fields and fresh foliage is, to any sensible extent, due to this 

 cause, it is quite certain that sun-heat is put out of existence 

 as heat, by the growth of plants in any locality ; and that 

 just as much heat, neither more nor less, is emitted from fires 

 in which the whole growth of any period of time is burned. 

 Coal, composed as it is of the relics of ancient vegetation, de- 

 rived its potential energy from the light of distant ages. 

 Wood fires give us heat and light which has been got 

 from the Sun a few years ago. Our coal fires and gas lamps 

 bring out, for our present comfort, heat and light of a primeval 

 Sun, which have lain dormant as potential energy beneath 

 seas and mountains for countless ages. 



We must look, then, to the Sun as the source from which the 

 mechanical energy of all the motions and heat of living crea- 

 tures, and all the motion, heat, and light derived from fires and 

 artificial flames, is supplied. The natural motions of air and 

 water derive their energy partly no doubt from the sun's heat, 

 but partly also from the earth's rotatory motion, and the rela- 

 tive motions and mutual forces between the earth, moon, and 

 sun. If we except the heat derivable from the combustion of 

 native sulphur and of meteoric iron, every kind of motion 

 (heat and light included) that takes place naturally, or that 

 can be called into existence through man's directing powers on 

 this earth, derives its mechanical energy either from the Sun's 

 heat or from motions and forces among bodies of the solar 

 system. 



In a speculation recently communicated to the Royal Society 

 of Edinburgh, the author had shown that the Sun's heat is pro- 

 bably due to friction in his atmosphere between his surface 

 and a vortex of vapours ; fed externally by the evaporation of 

 small planets in a surrounding region of very high tempera- 

 ture — which they reach by gradual spiral paths ; and falling 

 inwards in torrents of meteoric rain from the luminous atmo- 

 sphere of intense resistance, to his surface. 



