74 THE CLIMATE OF AUSTRALASIA 



variations ; and his 30 years' pursuit of the 

 rainfall cycle has at length been rewarded by 

 the most fruitful and suggestive results yet 

 obtained. 



The Lockyers' explanation of the apparent 

 caprice of the Indian rainfall is based on a 

 study of the spectra of all the sun spots that 

 have appeared since 1876. Their work has 

 enabled them to use sun spots as chemical 

 thermometers, showing the variations in the 

 temperature of the sun. The Lockyers have 

 studied the spectrum of every sun spot, since 

 1876, which was sufficiently large for spectro- 

 scopic measurement. The results show that 

 the sun spots indicate changes in the heat of 

 the sun, and are most numerous at periods of 

 intense solar activity, when the sun is hottest. 

 The Lockyers have found that at one time the 

 majority of the lines in the sun spot spectrum 

 are referable to elements which are known to 

 exist upon the earth ; they therefore are called 

 the " known" lines. At other times the 

 majority of the lines in a sun spot spectrum do not 

 occur in the spectra of elements known upon 

 the earth's surface. When these unknown lines 

 are predominant in the spectrum, the lines are 

 wider apart, indicating that the temperature of 

 the sun at that period is hotter than when the 

 lines are close together. The increased heat, 

 the Lockyers suggest, breaks up some of the 

 elements in the sun, and so the spectrum of 

 such material is different from that given by it 



