ADDITIONS TO THE NEWTONIAN THEORY. 469 



be found that with regard to some of these stars, and y Virgiuis in 

 particular, the conformity of the observations with the laws of ellipti 

 :al motion amounts to a degree of exactness which must give astron 

 omers a strong conviction of the truth of the law. For since Sir "W 



o 



Herschel's first measures in 1781, the arc described by one star about 

 the other is above 305 degrees; and during this period the angular 

 annual motion has been very various, passing through all gradations 

 from about 20 minutes to 80 degrees. Yet in the whole of this change, 

 the two curves constructed, the one from the observations, the other 

 from the elliptical elements, for the purpose of comparison, having a 

 total ordinate of 305 parts, do not, in any part of their course, deviate 

 from each other so much as two such parts.] 



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 magnitude 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 extended to the 

 all but infinite distance of the fixed stars, presses upon our minds with 

 a strong claim to be accepted as a universal law of the whole material 

 creation. 



Thus, in this and the preceding chapter, I have given a brief sketch 

 of the history of the verification and extension of Newton's great dis- 

 covery. By the mass of labor and of skill which this head of our sub- 

 ject includes, we may judge of the magnitude of the advance in our 

 knowledge which that discovery made. A wonderful amount of talent 

 and industry have been requisite for this purpose ; but with these, ex- 

 ternal means have co-operated. Wealth, authority, mechanical skill, 

 the division of labor, the power of associations and of governments, 

 have been largely and worthily applied in bringing astronomy to its 

 present high and flourishing condition We must consider briefly what 

 has thus been done. 



