Btmospbere* 45 



evaporation and cloud formation. It is not 

 enough that we have the air in which we live 

 and move, with all of its properties, as we have 

 described : something more is needed which is 

 absolutely essential both to animal and vege- 

 table life and this essential is motion. If 

 the air remained perfectly still with no lateral 

 movement or upward and downward currents 

 of any kind, we should have a perfectly con- 

 stant condition of things subjected only to 

 such gradual changes as the advancing and re- 

 ceding seasons would produce owing to the 

 change in the angle of the sun's rays. No 

 cloud would ever form, no rain would ever 

 fall, and no wind would ever blow. It is of 

 the highest importance not only that the wind 

 shall blow, but that comparatively sudden 

 changes of temperature take place in the at- 

 mosphere, in order that vegetation as well as 

 animal life may exist upon the surface of the 

 globe. The only place where animal life could 

 exist would be in the great bodies of water, 

 and it is even doubtful if water could remain 

 habitable unless there were means provided 

 for constant circulation motion. 



The mobility of the atmosphere is such that 

 the least influence that changes its balance 

 will put it in motion. While we can account 

 in a general way for atmospheric movements, 

 there are many problems relating to the details 

 that are unsolved. We find that even the 



