168 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1913. 



To throw light on this point Mrs. Maunder associated on each 

 half of the disk the tAvo extreme zones and compared the nmnber of 

 groups of spots which had been seen in each of the two double zones. 

 The predominance was clearly in the eastern pair. There are 

 throughout a cycle more spots seen near the eastern border, and 

 consequently for the whole visible hemisphere and whole cycle there 

 is an excess of disappearances over appearances of spots. The oppo- 

 site must hold on the invisible hemisphere^ since at the beginning 

 and end of a cycle the sun is entirely free from spots. 



Neglecting the extreme zones, where the disappearances may be 

 more subject to error, there was obtained for each zone the number 

 of spots which were seen in it for the first time and the number seen 

 in it for the last time. The following result was noted : 



As we go from east to west, crossing the visible hemisphere, there 

 is an almost constant diminution in the number of spot appearances 

 over a whole spot cycle and as nearly constant and even greater aug- 

 mentation in the number of disappearances. 



T\'lien we compare two symmetrical regions of the disk, the number 

 of births found in one is generally smaller than the number of dis- 

 appearances in the corresponding region on the other side of the cen- 

 tral meridian. 



If we were dealing only with numbers, the departures noted might 

 be considered as resulting from a psychological cause. It is probable 

 that there is in an observer a certain, perhaps unconscious, laziness 

 which keeps him from recording new appearances and prolonging 

 old spots unless absolutely necessar3^ It is always more agreeable 

 to register a disappearance which simplifies work rather an appear- 

 ance which augments it. 



Thus, when a new small spot appears for the first time, there is 

 a tendency to include it among those already noted rather than to 

 regard it as an advance guard or germ of a new group. If the first 

 impression is wrong, then there results an unjustified diminution of 

 births in the visible hemisphere. 



In a similar manner, if a small group approaches a more important 

 group, either by expansion or derivation, there will be a tendency 

 not to consider it separately and to cease counting it as soon as the 

 separation between it and the larger group ceases to be distinct. We 

 are thus led to credit fictitious disappearances to the visible hemi- 

 sphere. 



Both these considerations lead us to record more disappearances 

 than births. But these errors in counting do not explain why the 

 total area of spots is regularly found greater in the eastern half of 

 the visible disk. Considering all of Mrs. Maunder's results we are 

 led to think that the presence of the earth above the horizon of a 

 place on the sun tends to make spots there disappear. 



