LAWS OF HEAT. AIR. 101 



variety, we have two antagonist forces, by the 

 struggle of which such changes occur. Steam 

 and air, two transparent and elastic fluids, ex- 

 pansible by heat, are in many respects and pro- 

 perties very like each other. Yet, the same heat 

 similarly applied to the globe, produces at the 

 surface currents of these fluids, tending in oppo- 

 site directions. And these currents mix and 

 balance, conspire and interfere, so that our trees 

 and fields have alternately water and sunshine ; 

 our fruits and grain are successively developed 

 and matured. Why should such laws of heat and 

 elastic fluids so obtain, and be so combined ? Is 

 it not in order that they may be fit for such 

 offices? There is here an arrangement, which 

 no chance could have produced. The details of 

 this apparatus may be beyond our power of 

 tracing ; its springs may be out of our sight. 

 Such circumstances do not make it the less a 

 curious and beautiful contrivance : they need not 

 prevent our recognizing the skill and benevolence 

 which we can discover. 



2. But we have not yet done with the ma- 

 chinery of the weather. In ascending from the 

 earth's surface through the atmosphere, we find 

 a remarkable difference in the heat and in the 

 pressure of the air. It becomes much colder, and 

 much lighter ; men's feelings tell them this ; and 

 the thermometer and barometer confirm these 



