( 4^9 ) 



8irrf<(ce Iiifer/raJs in Meteorology. 



Bv Francis E. Nipher. 



This country is now so well provided with observers of tem- 

 perature and rainfall that it is easy to ch\aw lines of equal rainfall 

 and temperature with great precision. 



Some years since the writer began an examination of the rela- 

 tion between the amount of water falling upon various sections 

 of the Mississippi and its tributaries and the amount of water 

 discharged from that area in the rivers. It was found, for exam- 

 ple, that the rainfall in cubic feet upon the state of Missouri dur- 

 ing the two years ending in iSSS was exactly equal to the water 

 flowing past St. Louis in the Mississippi river, as determined 

 from the daily gauge readings. 



It is evident that a similar integration of rainfall over the 

 United States will be a very stable quantity, and it is a matter of 

 great interest to learn how much this quantity varies from year to 

 year. I have applied this method to the ten-year rain charts of 

 the Signal Service which cover the period ending in iSSo. The 

 map areas were determined by the planimeter. The rainfall be- 

 tween the nine-inch line and the ten-inch line was asssumed to 

 be nine and a half inches. The scale of the map was determined 

 by measuring the map areas of a group of states whose areas in 

 ■square miles may be considered as well known. The amount 

 of water in cubic feet is then easilv determined by a summation 

 of such integrals. Where the lines closed upon themselves 

 around maximum or minimum areas, special methods of deter- 

 mining the rainfall to be assigned were used, which it is unneces- 

 sary to explain here. 



The results for the whole country in cubic miles of wa- 

 ter are — 



