i4 

 Evaporating power of the air and sunshine . 



The two-week graphs of the values for atmospherj, c 

 evaporating, ptjwer and sunshine will be treated together 

 since '•"'^^ seasonal ""i-ar-'hes nf these two clinatio ccnfl i *:" npp. 

 exhibit the same general characteristics. Three points .nay 

 be noted in regard to the seasonal marches of these two 

 climatic indices. (1) Both grapHq have, in -Rneral, a dovm- 

 v/ard slope from the beginning to the end oi the season. 

 (Z) In the majority of cases they agree in direction of slope, 

 from v-pr^od to pp'r'od, throughout the sef^so-;^:. f5) The;' agree 

 in having a primary maximum, with a very high value, fo? the 

 early periods of the season and one or more secondary maxima, 

 with lov/er values, f c - i^eriods ^ha'^ occur later. The second- 

 ary maxima of the graphs for light and evaporation sometimes 

 (but not always) coincide, as to time of occurrence, with a 

 corresponding ms^i'nnTi or" the graph for temperatore efficiency. 

 The following consideration of the individual station graphs 

 for these two conditions may serve to bring out these points. 



■Por Oakland the primary .-'H-v-im-am 'n th^ frraph of atmos- 

 pheric evaporating power fl53) occurs for the first period 

 (beginning May 27)). The value of the evaporation index then 

 decreases steadily to a relative magni t-!i,i<^ nf 7Q fnr the +"irst 

 two weeks in July, after which it increases to a maximum (104) 

 which corresponds in time of occurrence (period beginning 

 July 6) -^(^ ^he second maxim^im of "^hp graph 6f temperature 

 efficiency. After passing this maximiim th6 graph descends 

 again, to the lo- values 57 and 69 for the last two netiods 

 (beginning August £7 and Sept. IE). The sunshine intensity 



