ASTRONOMY. %tf 



c. Algol, or /3 Persei, has been observed to have pe- 

 riodical changes of brightness, that return at the 

 distance of about 2 days and 21 hours. At its 

 greatest brightness, it is of the second, at its least, 

 of the fourth magnitude ; the change from the first 

 state to the second is made in about three hours 

 and a half, and the change back again in the same 

 time ; during all the rest of the period it pre- 

 serves its greatest brightness, Phil. Trans. 1773. 

 Also VINCE, 713. 



Some other stars are subject to similar variations. 



36. Though the fixed stars are without sensi- 

 ble motion relatively to one another, yet many 

 of them, when observed very accurately, are 

 found to change their places slowly. 



This was suspected by MAYER, but was first proved 

 by Dr MASKELYNE. 



Thus the right ascension of Sirius diminishes annu- 

 ally by two thirds of a second, and his declination, 

 (which is south), increases by 1".2. Something of 

 the same kind is observed of several others. VINCE, 

 724-. Whether this motion is always in the same 

 direction, or always at the same rate, is not yet 

 known. 



37. In many places of the heavens, spaces 

 faintly luminous, or shining with a pale white 



light, 



