126 



gram no crossing of the iron and "unknown" lines had occurred 

 though normally to be expected. These unusual solar condi- 

 tions prevailing in 1897 to 1900 were accompanied by irregular- 

 ities in the rainfall in India, and may perhaps also be reflected 

 in the somewhat unusual irregularities in the rainfall records 

 and hydrograph in Illinois during this period. The data avail- 

 able for the discussion of the periodicity of rainfall are so lim- 

 ited that only tentative values can be given to any conclusions 

 upon the subject. The striking conformity of the Illinois data 

 to the Lockyers' cycle will perhaps justify this discussion. 



As might be expected, the variation in the rainfall for 

 any given point of observation may far exceed that of the 

 average for the whole state. Thus we find a record of 74.5 

 inches for Muscatine, Iowa, in 1851, while its lowest record is 

 23.6 — a range of 50.9 inches. These extreme records are gen- 

 erally due to local rains of considerable magnitude, which are 

 often the cause of the sudden floods in the tributary streams 

 of the Illinois. 



The seasonal distribution of the rainfall for Illinois is 

 shown in the following table taken from Leverett ('96). 





Spring 



Summer 



Autumn 



Winter 



Annual 



Cubic miles 





10.2 



II. 2 



9.0 



7-7 



38.1 



34-0 



The distribution by months, expressed in percentages of the 

 total, is as follows. 



I 



II 



6.7 



III 



IV 



V 



VI 



VII 



9.9 



VIII 



IX 



X 



XI 

 7-i 



XII 



6.2 



7.0 



8.2 



10.4 



[2.2 



8.6 



9.0 



8.5 



6.0 



The table shows a minimum in December with a gradual 

 increase to a maximum in June, from which the decline is 

 rapid, with only a slight interruption at the autumnal equinox. 



The tables given above apply to the state as a whole. An 

 examination of the individual records shows that the south- 

 ern part of the state has a somewhat greater rainfall than the 



