A BELT OF SUN-SPOTS. 



183 



spectrum. In a communication to the French Academy of Sciences, 

 M. Thollon says that an hour before his observation on the C-line he 

 had observed in the same region a slighter displacement not only of 

 the lines of hydrogen and of the 5-group but also of the coronal line 

 1,474. He observed on several days other remarkable spectroscopic 

 phenomena, and noticed that nearly the whole southern half of the 

 sun's disk gave manifest signs of violent agitation. In view of these 

 facts, it seems surprising that little apparent effect was produced upon 

 the earth by these solar outbursts. Two or three times in 1882 the 

 earth responded instantly with magnetic storms and brilliant auroral 

 displays to the solar activity, but this year the great sun-spots and their 

 accompanying phenomena have shown comparatively little power to 

 affect terrestrial magnetism. 



Fig. 1 shows the sun as it appeared on the 16th of July, when 

 the advancing procession of spots had reached two thirds of the way 

 across the disk. 



Fig. 2 represents the sun on the 20th of July, when the spot belt 

 extended completely across the disk. 



Fig. 3. 







Fig. 3 shows the appearance of the sun on the 25th of July, when 

 more than half of the procession had disappeared around the western 

 edge, and the great group bringing up the rear was near the meridian. 



In the latter part of August and early in September a row of spots, 

 principally in the southern hemisphere, was again seen upon the sun, 

 but it was shorter, more crooked, and composed of fewer spots and 

 groups, than the great belt of July. 



There is one point of view from which the sun-spot belt just de- 



