288 FRAQMENT8 OF SCIENCE. 



isli 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 produced 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 vaporization, lifts mechanically 

 all the moisture of our air, which when it condenses 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 fur- 

 nishes materials for glaciers. But the sun again inter- 

 poses, 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 toward 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 performs, 

 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 transparent carbonic acid gas, 

 formed by the falling together of carbon and oxygen. 

 The atoms thus in close union resemble our lead weight 

 while resting on the earth; but we can wind up the weight 

 and prepare it for another fall, and so these atoms can be 

 wound up and thus enabled to repeat the process of com- 

 bination. In the building of plants carbonic acid is the 

 material from which the carbon of the plant is derived; 

 and the solar beam is the agent which tears the atoms 

 asunder, setting the oxygen free, and allowing the carbon 

 to aggregate in woody fiber. Let the solar rays fall upon a 

 surface of sand; the sand is heated, and finally radiates 

 away as much heat as it receives; let the same beams fall 

 upon a forest, the quantity of heat given back is less than 

 the forest receives; for the energy of a portion of the sun- 

 beams is invested in building the trees. Without the sun 



* Kant surmised an action of this kind. 



