VOL. XXIII.] PHILOSOPHICAL TRANSACTIONS. 79 



was then either gone off the sun's disk^ or if it adhered to the limb, the great 

 tremuJation of the atmosphere hindered me from seeing it. 



Astronomers, by these spots, have found, that the sun revolves on its axis, 

 so as that in 27 days the same point in the sun's disk returns to the same place, 

 seen from the earth ; hence its semirevolution in 134- <^'iyS} and consequently 

 the spot going off the sun's disk the 19th of June, may be expected to return the 

 2d of July next to the eastern limb of the sun's visible hemisphere, if it be not 

 dissolved before that time. 



June the 26th, 1 "03, in the evening, I looked to see whether there were gene- 

 rated any new spots in the sun, but found none; but on the 27th, about ha'lfan 

 hour after 8 in the morning, by receiving the sun's image on white paper from 

 the 6-foot telescope, I saw a spot near the sun's vertical, towards the lower 

 limb. Between 9 and 10 I elevated the 1 6-foot tube, the clouds being now of 

 a convenient thickness to let me view the sun without prejudice to my eyes, 

 and found that this spot was of a triangular form, and that it was accompanied 

 with two other smaller ones; the sides of the great spot were curvilinear, this 

 with two smaller ones made an equicrural triangle. At 4 in the afternoon the 

 triangular spot had a small fragment separated from it, and itself was now be- 

 come elliptical. At half an hour after 5, the fragment from the great spot was 

 itself divided into two, and at half past 6 o'clock, there was a small fragment 

 separated from the lower end of the great spot. The observations made this 

 afternoon with the 1 6-foot glass, were when the air was clear, and to secure my 

 eye, the eye-glass was smoked with a wax candle. 



The 28th, about 7 in the morning, I saw that the great spot was much aug- 

 mented, but the smaller ones, that yesterday attended it, were vanished, and 

 that there were two new ones generated at about 1^ minute's distance from the 

 great one below, and towards the left hand of it; the great one was a parallelo- 

 gram, with a very black diagonal crossing, it. At lO o'clock, there was another 

 diagonal crossing the former, and the two smaller spots, which before were long- 

 sh, had now taken a round form. 



Some Observations on the Spots of the Sun. By the Rev. Mr. tVilliam Derham^ 



F.R. S. N°288, p. 1504. 

 Mr. Derham saw the same spots as Mr. Gray. Since the last appearance of 

 the solar spots, says he, I have invented and provided myself with a very nice 

 micrometer, and a watch that beats half seconds, hoping to have been able to 

 have seen another revolution of them. My micrometer is not, as usually, to 

 be put into a tube; but is to measure the species of the sun on paper, of any 

 radius, or to measure any part of it, which I am inclined to think is more exact 



