523 



LECTURE XLIV. 



ON THE APPEARANCES OF THE CELESTIAL BODIES. 



tVe are next to proceed to examine the sensible effects produced by those 

 motions which we have first considered in their simplest state, and after- 

 wards with regard to their causes and their laws. Many authors have 

 chosen rather to pursue a contrary method, and have attempted to imitate the 

 original and gradual developement of the primitive motions from their apparent 

 effects. But no conception is sufficiently clear, and no memory sufficiently 

 strong, to comprehend and retain all these diversified appearances with accuracy 

 and facility, unless assisted by some previous idea of the real changes which 

 produce them, or by some temporary hypothesis respecting them, which may 

 have been of use in its day for the better connexion of the phenomena, 

 although it does not at present deserve to be employed for a similar purpose, 

 in preference to simpler and better theories, which happen to be historically 

 of a later date. 



The proper motions of the fixed stars, as they are subjected to our obser- 

 vation, undergo two modifications; the one from the relative direction of 

 the motion, by which it may be more or less concealed from our view; the 

 other from the proper motion of the sun, and the planets attending him. 

 This motion has indeed only been inferred from the apparent motions of a 

 great number of stars, which are either partly or ro Uy referable to it, and 

 which could scarcely i'ave agreed so correctly as they do, if they had arisen 

 from the real and separate motion of each star. _ 



Among the motions of the primary planets, that of the earth itself requires 

 a principal share of our attention. The apparent places of the fixed stars are 

 not sensibly affected by the earth's annual revolution: if any of them had been 

 considerably less remote tlian they are, it is probable that this motion would 



