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LIGHT SCIENCE FOR LEISURE HOURS. 



even in such and such a week or month, a great spot 

 will appear; but they can tell what years will be 

 characterised by many sun storms and what years by 

 few, for ten or twelve years in advance. The great 

 sun spots which have been seen during the last few 

 months were predicted at least twelve years ago ; and 

 astronomy is far better assured that in the years 1893 

 and 1894 there will be many large sun spots than 

 meteorologists are that next March will probably be 

 stormy and next June relatively calm. Yet scarce 

 half a century has passed since the periodicity of sun 

 spots began to be recognised, and not a quarter of a 

 century has passed since the theory was thoroughly 

 established. We do not even yet know why these 

 waves of sun spots pass in their long ten-yearly surge 

 over the vast surface of the sun. The Kepler of the 

 sun has done his work ; the Newton has yet to come. 

 The work of a solar Newton will be well worth doing, 

 even though he may not (as he probably will) bear 

 somewhat the same relation to Schwabe that the pro- 

 found Newton bears to the ingenious and laborious 

 Kepler. 



What a problem it is that lies before astronomers 

 when we consider what sun spots really mean ! The 

 great atmosphere of the sun, whose breath is flame, is 

 yet so cool compared with his intensely glowing surface 

 that it absorbs a large proportion of his light as well 

 as of his heat. It absorbs so much that it actually 

 changes his colour. There can be no manner of doubt, 

 from what Professor Langley has shown about the 



