SDNSPOTS AND SOME OF THEIR PECULIARITIES. 69 



would therefore seem to be absurd to suppose that the earth 

 should have any effect upon sunspots ; yet there is evidence of 

 at least an apparent effect. 



Quite early in my work at the Observatory I was impressed 

 with the frequency with which groups of spots appeared to 

 increase in size and compactness as they approached the centre 

 of the disc, and to break up and diminish in size after they had 

 passed it. This was evidently due in part to the fact that spots 

 when near the circumference of the sun are seen edgeways — 

 that is to say, they are not fully presented towards us as they 

 are when they are near the centre of the sun's disc — but are 

 seen foreshortened. But after careful correction for this effect 

 of foreshortening, it was still found that this tendency remained 

 for spots to be largest when east of the central meridian. 



The irregularities in the behaviour of groups of spots are so 

 great that it was impossible to come to any safe conclusion on 

 the subject until many years' observations had been accumulated ; 

 but in 1906 and 1907 Mrs. Maunder undertook an investigation 

 of the problem, and found that if the sun's surface be divided 

 into strips corresponding to the distance passed over by a spot 

 in a single day, then, on the whole, taking these strips or 

 " lunes " one by one, and comparing each lune on the east of 

 the meridian of the sun's centre with the corresponding one to 

 the west, the total spotted area in the eastern lune was always 

 greater than that of the corresponding western lune when the 

 totals were taken for a great number of years. 



But a much more striking effect is seen when simply the 

 numbers of spot groups and not their areas are taken. If we 

 compare the number of groups found in the corresponding lunes 

 east and west, the eastern lune always shows a greater number 

 of groups than the western. Or, to put the matter a little 

 differently, in the sunspot cycle which lasted from 1889 to 1901, 

 no fewer than 947 groups came round the eastern limb of the sun 

 into view of the earth, but only 777 passed out of sight from 

 the earth at the western limb into the invisible hemisphere. 

 During this period of 12 years, therefore, no fewer than 170 

 spot groups faded out in the course of their progress across the 

 disc more than came into existence, so that the earth was 

 apparently responsible for the extinction of about 170 groups — 

 that is to say, of more than one-sixth the whole number that 

 came into view at the east limb. 



This predominance of east over west is relatively much more 



