1825.] Rev. Mr, Emmett on the Sola)- Spots. 383 



astronomers to examine the phenomena. In the observations, I 

 have received much assistance from my triend Dr. Wasse, who 

 is a very good and careful observer. 



A small spot disappeared between the 8th and 9th of Decem- 

 ber last, at the western limb ; on the 9th, 1'', there was no trace 

 of it, nor of the feculae, which I had constantly seen about it. 

 On the 24th, P 45', there was no trace of the same spot on the 

 east limb ; but on the 29th, the intermediate days being cloudy, 

 it had advanced nearly half way over the disc. By this obser- 

 vation, the precise time is not ascertained ; yet it follows from 

 it, that the spot was invisible, at least 15 days. 



Feb. 4, 1825. — I discovered a cluster of spots : on the 12th, 

 1'' 30', the most easterly spot was very near the edge of the sun's 

 disc ; its breadth was extremely narrow ; it was observed with a 

 Newtonian reflector of six inches aperture, with powers of 70 

 and 120, until about 5'', when it was not more than its own 

 breadth from the edge of the disc, which certainly was not 4" 

 of a great circle. Now the apparent diurnal motion of a spot is 

 13° — 20' at a mean rate ; hence the v sine of the arc described 

 by a spot in 24 hours, being on the edge of the disc at the 

 beginning or end of the time, is 25",8816; from which data I 

 conclude, that the spot must have disappeared about Feb. 12"*, 

 10"^ astronomical time. On the following morning there was no 

 trace of it ; therefore, the computed time of its disappearing 

 cannot be far wrong. Feb. 28'', iJ-'', Dr. Wasse observed the 

 same spot, with an achromatic by DoUond, of three inches aper- 

 ture, and power about 150. The nucleus, or black spot, had 

 just entered, and the eastern part of the umbra was coincident 

 w ith the limb : its magnitude was certainly not 4" ; hence it 

 cannot have been on the disc above five or six hours ; but I will 

 suppose 12'' ; upon this hypothesis, it cannot have appeared 

 before 27^ 13" 30', which leaves 15^^ 3'' 30' for the time it 

 remained invisible. The observations cannot be minutely accu- 

 rate, because the spot came into view, and disappeared in the 

 night ; but calculating from the number of observations which I 

 have made upon the solar spots, during several years, I am cer- 

 tain the error cannot exceed five or six hours. I have not 

 employed a micrometer in calculating the short intervals of time 

 during which the spots could not be observed, because since 

 the extent of the radius of the path which the spots describe is 

 not known, such measures cannot be used without involving 

 hypothetical views ; the only certain plan is to observe the spots 

 when just upon the very edge of the disc, which may be done 

 during the long days in the summer, and it is on this account 

 that 1 wish to call the attention of astronomers to the subject, as 

 early as possible. Had the time, which 1 calculate to be 15 

 days, been but half the sun's period, the difi'erence would be 



