378 FEAGMENTS OF SCIENCE. 



of the ocean are in part dragged as a brake along the 

 surface of the earth; and as a brake they must dimin- 

 ish the velocity of .the earth's rotation.* Supposing 

 then that we turn a mill by the action of the tide, and 

 produce heat by the friction of the millstones; that 

 heat has an origin totally 'different from the heat pro- 

 duced by another mill which is turned by a mountain 

 stream. The former is produced at the expense of the 

 earth's rotation, the latter at the expense of the sun's 

 radiation. 



The sun, by the act of vaporisation, lifts mechanic- 

 ally all the moisture of our air, which when it con- 

 denses falls in the form of rain, and when it freezes 

 falls as snow. In this solid form it is piled upon the 

 Alpine heights, and furnishes materials for glaciers. 

 But the sun again interposes, liberates the solidified 

 liquid, and permits it to roll by gravity to the sea. The 

 mechanical force of every river in the world as it rolls 

 towards the ocean, is drawn from the heat of the sun. 

 No streamlet glides to a lower level without having 

 been first lifted to the elevation from which it springs 

 by the power of the sun. The energy of winds is also 

 due entirely to the same power. 



But there is still another work which the sun per- 

 forms, and its connection with which is not so obvious. 

 Trees and vegetables grow upon the earth, and when 

 burned they give rise to heat, and hence to mechanical 

 energy. Whence is this power derived? You see this 

 oxide of iron, produced by the falling together of the 

 atoms of iron and oxygen; you cannot see this trans- 

 parent carbonic acid gas, formed by the falling to- 

 gether of carbon and oxygen. The atoms thus in close 

 union resemble our lead weight while resting on the 



* Kant surmised an action of this kind. 



