VARIABLE STARS. 35 



and remotest forms in the celestial spaces, in one common 

 bond of sympathy and brotherhood. 



But the discovery of the law of gravitation, as applicable to 

 these distant worlds as well as to the orbs of our own planetary 

 system, naturally engenders the presumption that the whole 

 series of laws and general operations with which gravitation is 

 here necessarily connected, applies to them also, with little or 

 no modification. And a further inquiry will disclose celestial 

 phenomena which tend greatly to strengthen this presumption, 

 if not to convert it into a positive conviction. 



Contemplating our own solar system, we are struck with 

 the fact that revolutionary motion every where prevails. The 

 planets are constantly whirling upon their axes, and perform- 

 ing their grand orbitual circuits in the heavens. The sun him- 

 self rotates upon his own center, once in about twenty-seven 

 days. -This revolution has been ascertained by the periodical 

 variation of the position of spots on his disk. 



But several of the stars of our firmament exhibit a phe- 

 nomenon similar to this, from which our sun's rotatory motion 

 has been inferred. That is, they alternately, and in regular 

 periods, give forth a greater and a less degree of light, as 

 though they had a brightest side and a side of a less degree of 

 brightness, which were alternately, and at regular intervals, 

 presented to us by a revolution upon their axes. This is one 

 of the facts which have confirmed astronomers in the otherwise 

 very natural presumption, that the stars are suns like our own, 

 and whose apparent diminutiveness is only owing to their 

 immense distances. 



There are also many instances in which the varying relative 

 positions of t\YO or more stars are such as to indicate a revo- 

 lution aroinid each other, and around a common center. Some 

 of these stars have vast periods, as, for instance, the double 



