500 MR BALFOUR STEWART ON SUN-SPOTS AND THEIR 



approximate investigation, this line has been used as denoting sufficiently well 

 an ecliptical longitude at all seasons, and the behaviour of the spots has been 

 examined with reference to it. This difference is of less consequence, when 

 we reflect that solar spots occur in a zone extending not very far on either side 

 of the solar equator ; and therefore also not very remote from the plane of the 

 ecliptic. 



The motion of the spots, owing to rotation, is in these pictures from left to 

 right, and the earth or point of view from which the phenomena are observed, is 

 of course in that longitude which passes through the centre of the picture; so 

 that if any planet were 90° to the left of the earth, it would be opposite that por- 

 tion of the sun's disc corresponding to his left limb ; and if 90° to the right, it 

 would be next the right limb. 



The motion of the planets is also from left to right, so that Mercury and 

 Venus gain upon the earth, while on the other hand, the superior planets fall 

 behind to the left. 



In making this examination of sun-spots at Kew, it was soon seen both by 

 Mr BECKLEYand myself, that if the sun's disc be filled with spots at any period, 

 and if one of these begins to heal up before passing the central line, another does 

 the same ; if again, the disc be empty of spots, and one breaks out on the right- 

 hand side of the disc, another spot will break out on the same side, and not on 

 the left. 



So marked is all this, that I have been enabled to construct the following 

 table, from which it will be seen, that the same behaviour of spots often lasts for 

 a considerable period of time. 



In this table, the planets of which the action is investigated, are Mercury, 

 Venus, and Jupiter, — the first of which, although small, is very near the sun ; the 

 second, although farther from the sun, is much larger than the first ; while the 

 third is far ofip, but extremely large. 



The pictures (which comprise all those at Kew available for the purpose) 

 were examined by myself, and the result obtained was confirmed by a separate 

 examination by Messrs Beckley and Whipple of Kew Observatory. 



From groups (1), (2), (4), and (5), we find that when Venus is at or near 

 opposition, there are a good many spots, and their tendency is to increase in size 

 up to the centre, or somewwhat past it, and then decrease. 



Again, for groups (3), (6), (7), (8), Venus is at or near conjunction, and there 

 are few spots; while for group (3), where both Venus and Jupiter are in conjunc- 

 tion, we observe a tendency towards the breaking out of spots on the second half 

 of the disc. As far, therefore, as may be gleaned from this record, Venus is espe- 

 cially influential in promoting the formation of spots for that portion of the sun's 

 surface, which is receding from her, and in arresting this formation for that por- 

 tion which is approaching her. 



