270 HISTORY OF PHYSICAL ASTRONOMY. 



measured with much correctness,) and by inventing 

 a method which depended upon the whole body 

 of observations, and not upon selected ones only, 

 for the determination of the motion, has made his 

 investigations by far the most satisfactory of those 

 which have appeared. The result is, that it has 

 been rendered very probable, that in several of the 

 double stars the two stars describe ellipses about 

 each other; and therefore that here also, at an 

 immeasurable distance from our system, the law of 

 attraction according to the inverse square of the 

 distance, prevails. And, according to the practice of 

 astronomers when a law has been established, Tables 

 have been calculated for the future motions ; and we 

 have Ephemerides of the revolutions of suns round 

 each other, in a region so remote, that the whole 

 circle of our earth's orbit, if placed there, would 

 be imperceptible by our strongest telescopes. The 

 permanent comparison of the observed with the 

 predicted motions, continued for more than one 

 revolution, is the severe and decisive test of the 

 truth of the theory : and the result of this test 

 astronomers are now awaiting. 



The verification of Newton's discoveries was 

 sufficient employment for the last century; the 

 first step in the extension of them belongs to this 

 century. We cannot at present foresee the mag- 

 nitude of this task, but every one must feel that 

 the law of gravitation, before verified in all the 

 particles of our own system, and now probably 



