188 MR. JOSEPH BAXENDELL ON THE 



the group. Some of these new spots occasionally increase 

 in size until they equal or even exceed the principal spots 

 of the sub-groups. In such cases, however, the latter 

 generally diminish, and the whole group undergoes consi- 

 derable changes; but amidst all these changes there appears 

 to be a constant tendency of the forces which produce the 

 spots to concentrate in two places in the group at some 

 considerable distance apart, and lying in a direction which 

 is evidently more or less dependent upon that of the sun's 

 rotation ; and it often happens that groups which have 

 apparently quite lost their original binary character again 

 resume it before their final decay and extinction. 



The preceding sub-group of binary groups is almost 

 invariably the first to appear, and generally the last to 

 disappear, the exceptions in the first case being fewer than 

 in the latter. 



Mr. Williamson's diagrams have proved very valuable 

 in afibrding many cases of groups which exhibit a deci- 

 dedly binary character ; and from the descriptions of the 

 solar spots given by former observers there can be little 

 doubt that groups of this class have at all times been of 

 common occurrence. Thus T may quote as an instance an 

 observation by Sir William Herschel, which will be found 

 recorded at p. 272 of the Phil. Trans, for 1801, and which 

 is an excellent illustration of one of the most interesting 

 phases of these binary groups. It is as follows : 



"January 18, 1801. Between two clusters of openings 

 near each other, there are some, as I suspect, incipient 

 openings : they resemble coarse pores of indentations. 

 January 19, 1801. The incipient openings between the 

 clusters of yesterday's observations are completely turned 

 into considerable openings. It seems as if an elastic but 

 not luminous gas had come up through the pores or inci- 

 pient openings, and spread itself on the luminous clouds, 

 forcing them out of the way, and widening its passage." 



