ON THE ORIGIN OF THE PLANETARY SYSTEM. 175 



The showers of stars, as examples now taking place 

 of the process which formed the heavenly bodies, are 

 important from another point of view. They develop 

 light and heat; and that directs us to a third series 

 of considerations, which leads again to the same goal. 



All life and all motion on our earth is, with few 

 exceptions, kept up by a single force, that of the sun's 

 rays, which bring to us light and heat. They warm 

 the air of the hot zones, this becomes lighter and 

 ascends, while the colder air flows towards the poles. 

 Thus is formed the great circulation of the passage- 

 winds. Local differences of temperature over land and 

 sea, plains and mountains, disturb the uniformity of 

 this great motion, and produce for us the capricious 

 change of winds. Warm aqueous vapours ascend with 

 the warm air, become condensed into clouds, and fall 

 in the cooler zones, and upon the snowy tops of the 

 mountains, as rain and as snow. The water collects in 

 brooks, in rivers, moistens the plains, and makes life 

 possible ; crumbles the stones, carries their fragments 

 along, and thus works at the geological transformation 

 of the earth's surface. It is only under the influence 

 of the sun's rays that the variegated covering of plants 

 of the earth grows ; and while they grow, they accumu- 

 late in their structure organic matter, which partly 

 serves the whole animal kingdom as food, and serves 

 man more particularly as fuel. Coals and lignites, the 



