4:82 HISTORY OF PHYSICAL ASTRONOMY, 



rected by the best formulae which are known ; and if the result o( 

 such a reduction leaves any thing unaccounted for, the astronomer is 

 forthwith curious and anxious to trace this deviation from the expected 

 numbers to its rule and its origin ; and till the first, at least, of these 

 things is performed, he is dissatisfied and unquiet. The reference of 

 observations to the state of the heavens as known by previous researches, 

 implies a great amount of calculation. The exact places of the stars 

 ut some standard period are recorded in Catalogues ; their movements, 

 according to the laws hitherto detected, are arranged in Tables ; and 

 if these tables are applied to predict the numbers which observation 

 on each day ought to give, they form Ephemerides. Thus the cata- 

 logues of fixed stars of Flamsteed, of Piazzi, of Maskelyne, of the As- 

 tronomical Society, are the basis of all observation. To these are ap- 

 plied the Corrections for Refraction of Bradley or Bessel, and those 

 for Aberration, for Nutation, for Precession, of the best modern astron- 

 omers. The observations so corrected enable the observer to satisfv 

 himself of the delicacy and fidelity of his measures of time and space; 

 his Clocks and his Arcs. But this being done, different stars so ob- 

 served can be compared with each other, and the astronomer can then 

 endeavor further to correct his fundamental Elements ; his Catalogue, 

 or his Tables of Corrections. In these Tables, though previous dis- 

 covery has ascertained the law, yet the exact quantity, the constant or 

 coefficient of the formula, can be exactly fixed only by numerous obser- 

 vations and comparisons. This is a labor which is still going on, and 

 in which there are differences of opinion on almost every point; but 

 the amount of these differences is the strongest evidence of the cer- 

 tainty and exactness of those doctrines in which all agree. Thus Lin- 

 denau makes the coefficient of Nutation rather less than nine seconds, 

 which other astronomers give as about nine seconds and three-tenths. 

 The Tables of Refraction are still the subject of much discussion, and 

 of many attempts at improvement. And after or amid these discus- 

 sions, arise questions whether there be not other corrections of which 

 the law has not yet been assigned. The most remarkable example of 

 such questions is the controversy concerning the existence of an An- 

 fc nual Parallax of the fixed stars, which Briukley asserted, and which 

 Pond denied. Such a dispute between two of the best modern ob- 

 servers, only proves that the quantity in question, if it really exist, is 

 of the same order as the hitherto unsurmounted errors of instruments 

 and corrections. 



[2d Ed.] [The belief in an appreciable parallax of some of the fixed 



