THE SPOTS ON THE SUN. 



4? 



When we look at the sun through clouds, or through a darkened 

 glass, it appears as a uniform disk of light. But, when we look at it 

 through a telescope of moderate magnifying power, the uniformity of 



Fig. 1. 



Tie Changes in the Appearance of a Spot, caused by the Rotation of the Snn. 



surface disappears, and we see it irregularly sprinkled with dark points 

 known as solar spots. These are, however, not always seen ; some- 

 times the solar disk is perfectly clear. It has heen found that for a 

 period of ten years, from 1840 to 1850, out' of a total number of 1,982 

 10 



