THE WEATHER CYCLE 



53 



no rivers flowing out of them, all act as rain 

 gauges for their drainage basins ; and Bruckner 

 found that the levels of other inland lakes, with- 

 out outlets, also varied in cycles of the same 

 length, and reached their maximum at about 



FIG. 9. The variations in depth of the water in Lake George. (From 

 Russell). 



the same dates as the Caspian. Bruckner 

 therefore considered the rainfall of 32 1 localities, 

 some of which have rainfall records for over two 

 centuries. Thus the rainfall data of Paris go 

 back to 1691. Bruckner's study of the rainfall 

 convinced him that it also varies in a cycle of 



