64 



E. WALTER MAUNDER^ f.R.A.S., ON 



for 14 days while crossing the disc, and diirins: the last 45 years 

 there have only been four other spots of the same order 

 naagnitude : of which, as it happens, two formed in the year 

 (1917) just past. It will, therefore, be seen at once that no great 

 power of diminishing the solar radiation can be ascribed to sun- 

 spots ; it is perfectly true that many spots are large, as compared 

 with the earth, but even the very largest can have but little 

 efJect upon the total radiation of the sun. 



Further, since the bright markings of the sun — the faculae — • 

 which are largely connected with sunspots, are brightest, largest, 

 and most numerous at the very same time when the spots are 

 darkest, largest and most numerous, it follows that any loss of 

 radiation frona the sun at the time of sunspot maximum is 

 compensated by the fact that that very time is the time of the 

 maximum of faculae ; indeed, the evidence appears to point to 

 an over-compensation, so that the time of maximum sunspot 

 activity would appear to be also the time of maximum radiation. 



However great, therefore, the actual scale of the disturbances 

 of which we see the evidence in the outbreaks of spots and faculae, 

 their scale is so small as compared with that of the entire sun 

 itself, that they can but represent a variation in the sun's total 

 output of light and heat which is relatively insignificant. It is, 

 therefore, not a very hopeful task to inquire as to whether we 

 have any evidence of a direct effect upon the earth of these 

 changes in the sun's condition. 



Table II., which gives a comparison between the annual rain- 

 fall at Greenwich and the sunspot area year by year, shows 

 clearly that there is no intimate connection between these two 

 phenomena, and may be taken as typical of the result of most 

 of these inquiries. Some slight and doubtful evidence has been 

 adduced in favour of a dependence of Indian famines or tropical 

 cyclones upon the spotted area of the sun, but researches on 

 these lines have faUen into disfavour for a good many years 

 past. 



But the variations in the sun's spotted area are felt by the 

 earth in one manner at aU events. At Greenwich Obsen^atory , for 

 many years, and at many other observatories throughout the 

 world, certain " magnetic needles are kept in cellars or other 

 suitable chambers, screened as carefully as possible from the 

 sun's light and heat, and these respond sympathetically to the 

 solar changes. For, day by day, there is an oscillation in the 

 intensity of the earth's magnetism, and also in its direction. 



