60 De la Rue, Stewart, and Loewy on Solar Physics. [Feb. 2, 



longitude will be represented by the various radii proceeding from the 

 centre C, the angular difference between the two radii denoting the angular 

 difference between the two corresponding longitudes. If the observer 

 be stationed at the earth, all points of the solar surface will advance by 

 rotation from left to right across the visible disk ; while the radii vectores of 

 the inferior planets Mercury and Venus, which move faster than the earth, 

 will appear to the terrestrial observer to have a left-handed rotation, in 

 such a manner that the planet Venus will move from its place in the 

 diagram to opposition, and ultimately come round to conjunction from the 

 left. On the other hand, the superior planets, which move more slowly 

 than the earth, will appear to the terrestrial observer to have a right- 

 handed rotation, in such a manner that Jupiter will proceed from his place 

 in the diagram to opposition, and ultimately come round in conjunction by 

 the right. Also the point B, which occupies the central position of the 

 visible solar disk, will have the same heliocentric longitude as the earth. 

 Let us make the central longitude, or longitude corresponding to the posi- 

 tion of the earth at the time of observation, our meridian, and let us 

 reckon as negative all longitudes less than 180 to the left, and as positive 

 all those less than 180 to the right. In this way a spot or point of the 

 sun's disk, as it comes round by the left limb, will have the longitude 

 90, while, as it disappears by the right limb, its longitude will be -{-90. 

 Hence also the longitude of Jupiter in the diagram will be ACB, while 

 that of Venus will be + BCD. If the angle ACB is very large, we may say 

 that Jupiter is much to the left, and if BCD is large, we may say that 

 Venus is much to the right. In the examination to which the spots have 

 been subjected, it has been endeavoured to ascertain, as nearly as possible, 

 at what longitude any spot breaks out, or at what longitude it reaches its 

 maximum and begins to wane. Very often, however, we are not able to 

 assign the exact longitude of such an occurrence ; but yet, as will be seen 

 in the sequel, we are able to determine, in a general way, the behaviour of 

 spots. 



The examination was made in the following manner. Mr. Carrington's 

 original drawings were examined by two observers noting the behaviour of 

 each spot, and the results again compared with Carrington's published 

 maps, which give the behaviour of spots from day to day ; ultimately a list 

 was obtained, no spot available for comparison being left out. A similar 

 process was followed with regard to the Kew pictures. 



It is to be remarked, that in making the examinations of the Carrington 

 pictures, both observers were ignorant of the planetary configurations ; and 

 that although with regard to the Kew pictures one observer knew the 

 corresponding planetary configurations, yet his judgment, being checked 

 by his fellow-observer, could not be biassed by any previous speculative 

 views. 



In a Table given, showing the behaviour of sun-spots from the beginning 

 of 1854 to the end of 1864, it is seen that different spots occurring about the 



