ONE ELEVEN-YEAR PERIOD OF SUN-SPOT OBSERVATIONS. ]'.) 



These numbers were seen with power ioo. I sometimes put on a power of 

 200 and could see about half as many more spots, and when the air was very 

 good, nearly twice as many. But the display on August 27, 1870, exceeded 

 any other that I have ever seen. The hundred power showed 640 spots; and 

 with the 200 eye-piece I counted the astonishing number of 950 sun spots ! and 

 the air was not very good either ; if it had been, I am fully convinced that one 

 thousand spots might have been distinctly counted. There were fourteen groups, 

 one of which had 340 spots; another, 300. But what a change soon followed! 

 On September nth, thirty-one spots were all I could see with power 100 ; On the 

 21st, I counted 460 spots in six groups; on October 23d, near 300 were counted 

 in eleven groups. I perceived that the number was growing less, and partly 

 through fear that so much intense looking at the sun might injure my eyes, I dis- 

 continued a regular count of the spots; but I still made frequent observations 

 on the number and comparative size of the groups. 



For many months the groups continued as numerous as they had been; but 

 they were much smaller, and the number of spots not so great. But the spots 

 occasionally appeared by the hundred for two or three years. For instance, 

 August 17, 187 1, there were nine groups; five were small, one large, and three 

 very large — the number of spots being nearly 400. Again, May 5, 1872, fifteen 

 groups, eleven small and four large, with about 200 spots. March n, 1873, 

 there were eleven small groups and one large group. May 20, 1873, m y record 

 reads : "One little spot on western side of the sun — the least show of sun-spots I 

 have seen for several years." On May 6, 1874, were one small group and three 

 large ones. In two days they were "three small and one large." April 4, 1875, 

 " two or three little groups." July 22, 1876, "but few sun-spots lately." A 

 few in 1877, though often none at all. About fifty observations were made in 

 1878, none showing any spots except those on February 6th, March 15th, May 

 21st to 28th, June 23d, November 3d and 22d, and the passage of a large spot, 

 nearly 5,000 miles in diameter, across the the sun, from September 1st to 13th. 



By this time we are forcibly struck with a very prominent and singular fact 

 connected with sun-spots, namely, their periodical recurrence, which occurs about 

 every eleven years. If my idea is correct that the maximum of the period just 

 passed occurred about the last of August, 1870, it would seem that the time from 

 minimum to maximum is much shorter than that from maximum to minimum; 

 for, at many times in 1867 no spots were visible, by which I infer that to have 

 been about the time of minimum, or least show of spots, and the beginning of 

 another period, which probably has just closed, or is about ending. (Late obser- 

 vations show no increase of spots, but I am watching for them.) 



This paper would be incomplete without a more definite account of the 

 largest spots, many of which were visible to the naked eye (protected by a shade 

 glass). The first one thus seen in this period, was on April 18, 1870. It was of 

 an oblong shape, and, by careful measurement with a glass microneter of 200 

 lines to the inch, was 14,000 miles wide and 21,000 miles long, the penumbra 



