125 



rainfall in the region surrounding the Indian Ocean. They 

 have found that the mean solar temperature is followed by a 

 pulse of rainfall. These mean temperatures occur twice in 

 each sun-spot cycle of eleven years, at intervals varying from 

 four to seven years, and are accompanied by the crossing of 

 the iron and "unknown" lines in the solar spectrum. These 

 solar fluctuations in temperature produce atmospheric condi- 

 tions, especially over large continental and oceanic areas, 

 which result in rhythmic pulses of rainfall which have been 

 traced by these authors in the rainfall of India and the snow 

 upon the Himalayas, and in the rainfall of Batavia, Cape of 

 Good Hope, Mauritius, and Cordova. They have also correlated 

 them with the floods of the Nile and the famines in India. On 

 Plate VI. is a diagram taken from Lockyer ('01 ) which shows 

 by curves the fluctuations of sun-spots (which in a general way 

 coincide with solar-temperature changes), and of the iron and 

 "unknown" lines. To this has been added the plot of the rain- 

 fall in Illinois and the hydrograph of the Illinois River. As 

 shown in the diagram the mean temperature (crossing of the 

 iron and "unknown" lines) occurs twice in each sun-spot cycle, 

 once on the rise in sun-spots (and temperature) (+ pulse), and 

 once on the fall (—pulse). The location of the rainfall pulses 

 of India and elsewhere accompanying these mean temperatures 

 is indicated upon the diagram. 



A close correlation between these pulses of rainfall and 

 the fluctuations in rainfall in Illinois and in the hydrograph of 

 the Illinois River is at once apparent on inspection of the dia- 

 gram. The + pulses of 1892 and 1883, and the — pulse of 1876-77 

 are well defined, while that of 1888 is present though not so 

 pronounced. 



Similar pulses of rainfall may also be detected at some- 

 what similar intervals in the rainfall of Illinois in the period 

 not covered by the Lockyers' diagram, 1851-76. Thus + pulses 

 may be located in 1872, 1862, and I85I, and — pulses in 1865 and 

 1855 or 1858. Another — pulse is probably to be seen in the 

 heavy rainfall of of 1898, though according to the Lockyers' dia- 



