292 HISTORY OF PHYSICAL ASTRONOMY. 



Thus Lindenau makes the coefficient of Nutation 

 rather less than nine seconds, which other astro- 

 nomers give as about nine seconds and three 

 tenths. The Tables of Refraction are still the sub- 

 ject of much discussion, and of many attempts at 

 improvement. And after or amid these discussions, 

 arise questions whether there be not other cor- 

 rections of which the law has not yet been assigned. 

 The most remarkable example of such questions 

 is the controversy concerning the existence of an 

 Annual Parallax of the fixed stars, which Brinkley 

 asserted, and which Pond denied. Such a dispute 

 between two of the best modern observers, only 

 proves that the quantity in question, if it really 

 exist, is of the same order as the hitherto unsur- 

 mounted errors of instruments and corrections (z). 

 But besides the fixed stars and their corrections, 

 the astronomer has the motions of the planets for 

 his field of action. The established theories have 

 given us tables of these, from which their daily 

 places are calculated and given in our ephemerides, 

 as the Berliner Jahrbuch of Encke, or the Nau- 

 tical Almanac, published by the government of 

 this country, the Connaissance des Terns which 

 appears at Paris, or the Effemeridi di Milano. 

 The comparison of the observed with the tabular 

 place, gives us the means of correcting the coeffi- 

 cients of the tables ; and thus of obtaining greater 

 exactness in the constants of the solar system. 

 But these constants depend upon the mass and 



