NATURAL HISTORY. 



599 



large as the earth. It passed off 

 like the rest, without doing any 

 mischief. 



We were of course indebted to 

 the telescope for our first know- 

 ledge of the existence of such 

 spots. They were seen for the 

 first time in 1611; and nearly 

 about the same time by J. Fabri- 

 cius, at Wittenberg, by the Jesuit 

 Scheiner, and by Galileo. That 

 great man watched their course 

 with so much attention, and so 

 ■well developed their phenomena, 

 that very little has been since ad- 

 iled to the descriptions ^vhich he 

 gave, except more precise mea- 

 sures. The spots of the Sun are 

 at presentviewed with astronomi- 

 cal telescopes, in which the gi'eat 

 brilliancy of that star is mitigated 

 and not effaced, by the coloured 

 glass placed between the telescope 

 and the eye. There are in the in- 

 terior of the telescope, at the focus 

 of the object, some very fine 

 threads stretched crosswise, and 

 moveable parallely to each other, 

 by means of which the distance 

 of the spot from the nearest bor- 

 der of the Sun's disk may be as- 

 certained, which determines its 

 position on the disk at the mo- 

 ment of observation. By follow- 

 ing in this manner the same spot 

 for several days, it is perceived to 

 change its place. Its size also 

 varies much. The spots some- 

 times grow thinner, and disperse 

 ).frora one day to another : and 

 hence it is that, though last month 

 rather a large number was visible, 

 within these few days only two 

 are to be seen. But during the 

 whole time of their presence they 

 pursue a regular course, of which 

 the aspects are common to all. 



When they first come in sight, 



they appear on the Sun's border 

 like a slender thread. In propor- 

 tion as they advance towards the 

 middle of the disk, they appear, 

 from day to day, to enlarge in the 

 direction of their movement. 

 They then decrease periodically ; 

 and if they last long enough to 

 traverse the whole disk, they go 

 off by the opposite disk, narrow- 

 ing to a single thread. These ap- 

 pearances are evidently such as a 

 small body, adhering to a spheri- 

 cal surface, and revolving with or 

 upon that surface, must present. 

 The diminution of the spots, iu 

 })roi)ortion as they approximate 

 the borders of the disk, results 

 from this — that they then project 

 more obliquely, and are only seen 

 sidewise ; but when in the middle 

 of the disk they are seen in their 

 full extent. In fine, upon com- 

 paring tlie direction and rapidity 

 of their course, it soon becomes 

 evident that the supposition of 

 their adhering to the body of the 

 Sim is the only admissible one : 

 that course is so steady, that when 

 the same spot has been watched 

 for several days, all the other po- 

 sitions which it may take may be 

 predicted with certainty. On 

 thus tracing the I'oute of all those 

 which appear, it is ascertained 

 that they move in courses exact- 

 ly parallel, describing circles 

 which all have their centre on a 

 co]umon axis, passing through 

 the centre of the Sun. The size 

 of these circles varies on different 

 points of the disk, according to 

 the same laws as on a sphere ; 

 and the rate of movement is mo- 

 dified in such way, that all the 

 ciicles are run through in equal 

 times. This perfect concordance 

 of revolution in spots so change- 

 able 



