THE SPOTS ON THE SUN. H9 



tangled with one another, sometimes neatly truncated, or again spread 

 out with no distinct termination. Their head is generally turned 

 toward the centre of the nucleus. They are not unlike strokes of color 

 laid on with a painting-brush, very white near the head, and gradually 

 less brilliant toward the tail." Fig. 5 represents a group of solar spots, 

 in which this closely-meshed appearance of the ovoid bodies is im- 

 pressively presented; and in Fig. 6 we see the willow-leaf structure 

 stretching completely across the umbra and forming bridges of light. 



The dimensions of solar spots are as variable as their forms. Some 

 are very small, appearing under the highest magnifying power like 

 mere specks ; others are of enormous magnitude. Many have been 

 observed which measure from 30,000 to 100,000 miles in diameter, so 

 that, if they are truly chasms and gulfs in the luminous envelope of 

 the sun, our entire globe, as Guillemin remarks, would appear in their 

 depths no larger than a fragment of a rock rolled into the crater of a 

 volcano ! 



The changes which these bodies undergo are extraordinary. They 

 seem to have an order of development. Proctor says the formation of 

 a spot is usually preceded by the appearance of facuke. Then a dark 

 point makes its appearance, which increases in size, the penumbra! 

 fringe being presently recognized around it, and the distinction be- 

 tween the umbra and the penumbra being well defined. But, when 

 the spot is about to diminish, the edges lose their sharpness as if 

 screened by a luminous veil ; capes and promontories jut out, and 

 bridges of light are formed. Lockyer says sometimes changes are 

 noticed even within an hour. Their periods are most variable ; the 

 smallest merely appear and disappear, lasting a mere fraction of the 

 time of solar rotation. The larger live frequently during two rota- 

 tions, and Schwabe saw one which returned eight times, continuing 

 200 days. 



The remarkable changes that sometimes occur are well illustrated 

 in Fig. 7, which represents four drawings of the large spot that ap- 

 peared October 7, 1865, and which was more than 46,000 square 

 miles in area. The drawings are numbered in the order of date. 

 No. 1 exhibits the oblong, fore-shortened view presented when it first 

 appeared on the edge of the sun. No. 2 represents its aspect three 

 days afterward. No. 3 shows its appearance four days later, and No. 

 4 is a view of it on October 16th. 



Sometimes spots exhibit a rotatory or whirlpool appearance, as if the 

 solar envelope were subject to tremendous tornadoes. Fig. 8 represents 

 a spot seen and drawn by Secchi at Rome, May 5, 1857, which repre- 

 sents a vortex, into which the substance of the photosphere is rushing 

 with an eddying motion. De La Rue took two photographic pictures 

 of the same spot at an interval of two days, and, when these are placed 

 together and looked at through the stereoscope, the spot exhibits a 

 funnel-like concavity with remarkable exactness. There is other evi- 



