212 CELESTIAL MEASURINGS AND WEIGHINGS. 



right ascension." If that movement were coincident in 

 direction with such a parallel, there would remain no- 

 thing further to explain. But such is not the case. It 

 is oblique ; and may therefore be regarded as composed 

 of two movements, the one along that parallel (in right 

 ascension), the other perpendicular to it, or, as it is 

 technically called, " in declination." Now these move- 

 ments admit of a distinct and separate examination, and 

 it is clear that, if both do not agree in indicating the 

 same kind of undulation and the same identical period, 

 the explanation so afforded of what may be called one 

 half of the phenomenon is at variance with that of the 

 other. Mr Peters left this other half untouched; but 

 very recently that also has been examined by an Ameri- 

 can computist, Mr Safford, on the same principles ; and 

 the result is that the orbital motion, which accounts for 

 the one set of movements, gives at the same time a suffi- 

 ciently satisfactory explanation of the other. 



(38.) Here, then, we are furnished with another ex- 

 ample like that afforded by the grand discovery of the 

 planet Neptune by the calculations of Adams and Levep 

 rier. The existence of a celestial body not seen and not 

 before known to exist, has been revealed to us and its 

 orbit computed, by the simple application of mathema- 

 tical calculation grounded upon observed irregularities 

 in the movements of one already well known. 



(39.) The parallel of the cases promises to be still 

 closer. Neptune, as is well known, was immediately 

 sought and found in the place assigned to it by the cal- 

 culation. In January 1862, Mr Alvan Clark, an eminent 



