78 



It was Schwabe iii 1826 who first made an enumeration of sun- 

 spots, carefully Avatcliing the sun's sui-fjice from day to day. 

 Similar observations by others have been carried on from that 

 time to this, the result of the Avhole being the determination of a 

 period of rather more than eleven years as the cycle mthin which 

 the sun-spot variations, or the change from maximum to minimum 

 and then the change back to maximum again, take place. It 

 should be stated, however, that these two changes do not occupy 

 exactly equal times, " the period of increase from the minimum 

 to the maximum year in the sun-spot cycle being almost ahvays 

 shorter thau the period of decrease from the maximum to the 

 minimum." 



A connection between the variations of solar activity and 

 terrestrial magnetism has been well established for a long time back, 

 but it is only of recent years that a similar connection has been 

 thought to be traced between sun-spots and terrestrial meteorology. 

 It is due to Mr. Meldrum, Government Astronomer at Mauritius, to 

 have first drawn the attention of observers to this subject, as 

 bearing especially upon that particular class of phenomena which 

 we have been considering above. It is well known that the 

 Indian Ai-chipelago is the site of those fearfully destructive 

 cyclones which occur from time to time in the southern hemis- 

 phere, as the "West India Islands mark the region whence emanate 

 the tremendous hurricanes in the northern hemisphere, many of 

 which last crossing the Atlantic find their way to this country, 

 though generally losing much of their force before reaching our 

 shores. 



It is to these cyclones in the Indian Ocean that Mr. Mel- 

 drum has directed his attention in connection with the sun-spot 

 cycle. Noting down -with, great exactness the number and 

 intensity, as well as the times of occurrence, of all the cyclones 

 that took place there during a period of more than twenty years, 

 and then marking ^vith equal exactness the number and intensity 

 of the spots on the sun during the same period, he found there 



