Royal Society. 391 



by the various radii proceeding from the centre C, the angular dif- 

 ference between the two radii denoting the angular difference between 

 the two correspondin glongitudes. 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 ot 

 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 pla- 

 nets, 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 position 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 lon- 

 gitude 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 longi- 

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

 mum 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. Carring- 

 ton's original drawings were examined by two observers noting the 

 behaviour of each spot, and the results again compared with Car- 

 rington's published maps, which give the behaviour of spots from day 

 to day ; ultimately a list was obtained, no spot available for compa- 

 rison 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 Car- 

 rington pictures, both observers were ignorant of the planetary confi- 

 gurations ; 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 same time on the sun's disk behave themselves 

 in the same manner ; so that if one spot, after making its appear- 



