

OF THE COSMOS. PERIODICALLY VARIABLE STARS. 153 



Since all is in motion in the celestial canopy, and all 

 things are variable in space and in time, we are led by ana- 

 logy to conjecture, that as the fixed stars have all not merely 

 an apparent motion, but also a proper motion of their own, 

 so also their surfaces or luminous atmospheres may be gene- 

 rally subject to changes, which, in the case of the greater 

 number of these cosmical bodies, may occur in exceedingly 

 long, and therefore unmeasured, and perhaps indeterminable, 

 periods ; while, in the case of a few, they may take place 

 without being periodical, as by a sudden revolution, and for 

 a longer or shorter continuance. The latter class of phae- 

 nomena, of which a remarkable example is presented in our 

 own days by a large star in the Ship (rj Argus), will not be 

 discussed in this place, where we are about to consider only 

 stars variable within periods which have already been inves- 

 tigated and measured. It is important to distinguish from 

 each other three great sidereal phenomena, of which the 

 connection has not yet been recognised : viz. variable stars 

 of known periodicity ; the blazing forth of what are called 

 new stars ; and sudden changes of light in long-known fixed 

 stars, which had previously always shewn a uniform inten- 

 sity. I propose at present to dwell exclusively on the firsts 

 named form of variability, of which the earliest accurately 

 observed example (1638) is furnished by Mira Ceti, a star 

 in the neck of the Whale. David Fabricius, a minister of 

 the church in East Friesland, and the father of the disco- 

 verer of the solar spots, had, it is true, already observed this 

 star as of the 3rd magnitude, on the 13th of August, 1596, 

 and had noticed its disappearance in October of the same 

 year. But the alternately recurring change of light, or the 

 periodical variability of the star, was not discovered until 



