36 



extraordinary changes which a large spot was seen to undergo in 

 the course of a few days. It is a remarkable fact, too, concerning 

 them that they are scarcely ever observed at a greater distance 

 than thirty-five degrees north or south of the sun's equator. 



Eemembering the vast size of these cavities in the photosphere 

 and their rapid and singular changes, we may get some idea of the 

 enormous forces which are at work on the sun's surface. Winds, 

 storms, cyclones, there must be among these fiery clouds of the 

 sun. Uprushes of vapour hot from the fiery interior of the sun, 

 says M. Faye ; downrushes of cooler vapours from the exterior to 

 the interior, say the English astronomers. Whichever it be (and 

 all the more recent observations seem to point to the last as the 

 true explanation), it is certain that these storms partake of the 

 nature of the spiral storms, cyclones wliich are so frequent in tne 

 tropics. On the screen is a draT\"ing of a cyclonic sun-spot observed 

 by Father Secchi. 



We mil now pass on to the extraordinary discovery of the 

 periodicity of sun spots and their connection vni\\ terrestial phe- 

 nomena. About the commencement of this century Herr Schwabe, 

 of Nassau, set himself to observe diligently the face of the sun. 

 Hour after hour, daj' after day, whenever the sun was visible he 

 scrutinized its changing phenomena. After some years he dis- 

 covered that there were periods when these sjiots on the sun's disc 

 were greater in number and in magnitude than at other times. 

 After twelve years of work, he satisfied himself that the period of 

 maximum and minimum was about eleven years ; six years more 

 he spent to confirm that truth to himself, and again, thirteen more 

 to convince mankind. But that labour of thirty-one years estab- 

 lished the law of the sun-spot period as veiy nearly 1 1 years and 

 a quarter. During the time that Schwabe had been busy ex- 

 amining the sun at his little observatory at Nassau, General Sabine 

 had been no less industrious in examining the variations which 

 the magnetic needle underwent at Kew in consequence of thecur- 

 lents of electi'icity which at certain periods thrill through the earth. 



