THE WEATHER 



151 



changes on the earth; but as yet we know little that 

 is definite. 



Meanwhile studies of air movements and winds, and 

 of the moisture, heat, or cold they carry with them are 

 constantly being made by the United States Weather 



FIG. 77. Observatory on Mt. Rose, the highest on the Pacific (10,000 feet). 

 It is upon such observatories that future progress in weather study 

 largely depends. 



Bureau, and elsewhere in the world. Tlies^^ud^^elj) 

 us to understand weather changes. Thus we now know 

 that both storm and clear-weather areas are usually 

 in the form of great circular whirls of air (cyclones) 

 fifteen hundred to two thousand miles across. They 



