THE WEATHER CYCLE 75 



under any conditions yet produced on the 

 earth's surface. 



The proportion of the known and unknown 

 elements in the sun spot spectrum, of course, 

 vary inversely. When the proportion of the 

 known element is greatest, there is the lowest 

 proportion of the unknown lines. When the 

 numbers of the known and unknown lines are 

 equal, the sun's temperature is at its mean. 

 Accordingly the study of the sun spot spectra 

 determines whether the heat of the sun is above 

 or below the average. 



After the Lockyers had established this 

 point, their next step was to study the records 

 of the rainfall in Mauritius and India, to see if 

 these variations in the solar temperature had 

 any recognisable effect on the rainfall. When 

 the sun spots are most numerous, their spectra 

 show the greatest predominance of unknown 

 lines, and the solar temperature is therefore at 

 its hottest. It is found that at this period the 

 south-western monsoon gives India its maximum 

 of rainfall, while India, as a whole, being 

 continental, is under cyclonic conditions. At 

 the same time, Mauritius, being an oceanic 

 island, is naturally under anticyclonic conditions, 

 and has a minimum of rainfall. The maximum 

 rainfall at Mauritius occurs when the sun spots 

 and solar temperature are at their minimum, 

 and the island is under cyclonic conditions. 

 The rainfall curve of Mauritius is comparatively 

 simple, and shows an T i years cycle ; but the 



