392 Royal Society : — 



ance, increases until the centre line, another will do the same ; or 

 if one spot breaks out on the left or on the right, half the other 

 spots about the same period have a tendency to break out on the 

 same half. Examples of these are referred to in the Tables. 



The authors suppose that this peculiarity of behaviour of spots 

 can only be explained by reference to some influence from without. 

 Suppose that such an influence, of a nature unfavourable to spot- 

 production, exists, then, as spots are brought round to it by rota- 

 tion, they will gradually wane ; and, on the other hand, as the 

 surface departs from it, spots will break out. But while there is 

 good evidence for believing in the existence of some such influence, 

 it is a very difficult thing to determine its nature, and one which 

 can only be done very imperfectly with our present knowledge. 



The authors attempt to answer the following questions. Is this 

 influence stationary ? or, if moveable, can it be traced to any of the 

 planets of our system ? 



The behaviour of each series of groups is then compared with the 

 positions of the three planets, Mercury, Venus, and Jupiter, at the 

 same date ; these planets being imagined to be the most influential ; 

 since the first, though small, is ven r near the sun, tbe second is both 

 near and tolerably large, while the last, although distant, is of very 

 great mass. 



In answer to the first question, Is the influence stationary ? it 

 may be remarked that if it be so, the difference of behaviour noticed 

 at different periods must be due to the position of the earth, or point 

 of view at these periods with reference to the stationary influence, 

 and hence in similar months of different years we should have a 

 similar behaviour ; but it cannot be found from investigations that 

 there is any connexion between a certain behaviour of sun-spots and 

 a certain period of the year, and hence there is no reason to suppose 

 that the external influence is fixed. 



In the next place, does this influence, if moveable, move faster or 

 slower than the earth ? If faster, it will proceed from conjunction 

 to opposition, passing over the sun's disk from left to right. If we 

 view it as one unfavourable to the production of spots, then, at first, 

 when it is near conjunction, or a little to the left, the sun's surface to 

 the right, receding from it, will break out into spots ; but as the in- 

 fluence moves on to the right, spots will come towards it from their 

 first appearance, and will consequently decrease from the first. But 

 if, on the other hand, the influence move more slowly than the earth, 

 it will move from conjunction to opposition, from right to left ; so 

 that a tendency of spots to form on the disk will be followed by 

 a tendency to increase, not decrease, after making their appearane. 



The order of the consecutive phenomena will thus be different in 

 the two cases. 



It is shown by a Table that a tendency of spots to break out is fol- 

 lowed by a tendency of spots to decrease after making their appear- 

 ance, and it is thereby concluded that the influence moves faster 

 than the earth. This would seem to point to either Mercury or 

 Venus as the agent in this matter, but the behaviour varies too 



