CLIMATIC FACTORS : THE AIR 



99 



value that would include several factors operative in plant dis- 

 tribution, Transeau 255 used the ratio of precipitation to evapo- 

 ration (P/E) for plotting climatic zones. These zones match the 

 limits of vegetation types remarkably well, but the method is 

 limited by the availability of adequate and comparable evapora- 

 tion data. 



A graphic method for distinguishing differences and similari- 

 ties in atmospheric conditions is the climograph, in which mean 

 temperature is plotted against mean relative humidity by months, 

 and the points are connected to form highly distinctive twelve- 

 pointed figures. Introduced by Ball 11 for indicating climate of 



FlG. 46. Cup anemometer, Weather Bureau type, for relatively permanent 

 operation, and a Biram type anemometer, convenient for short-time measure- 

 ments.— Courtesy Friez Instrument Division, Bendix Aviation Corporation. 



