1865.] De la Rue, Stewart, and Loewy on Solar Physics. 61 



same time on the sun's disk behave themselves in the same manner ; so 

 that if one spot, after making its appearance, 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 rotation, 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 in- 

 fluence 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 posi- 

 tions 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 very near the sun, the 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 un- 

 favourable to the production of spots, then, at first, when it is near conjunc- 

 tion, or a little to the left, the sun's surface to the right, receding from it, 

 will break out into spots ; but as the influence moves on to the right, spots 

 will come towards it from their first appearance, and will consequently de- 

 crease 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 

 appearance. 



The order of the consecutive phenomena will thus be different in the two 



