126 LIGHT SCIENCE FOR LEISURE HOURS. 



planet, especially of one which had remained concealed 

 for so many centuries, must be regarded as at least as 

 interesting as the discovery of a planet altogether nn- 

 known. Nor was there any circumstance in the actual 

 discovery of Uranus, which would lose its interest, even 

 though we accepted quite certainly the conclusion that 

 the Herschelian planet was no other than old Kahu. 1 



Let us turn to HerscheFs own narrative of his detec- 

 tion of Uranus. It is in many respects very instructive. 



In the first place, we must note the nature of the 

 work he was engaged upon. He had conceived the idea 

 of measuring the distances of the stars, or at least of 

 the nearer stars, by noting whether as the earth circles 

 around the sun the relative positions of stars lying very 

 close to each other seemed to vary in any degree. To 

 this end he was searching the heavens for those objects 

 which we now call double stars, most of which were in 

 his day supposed to be not in reality pairs of stars 

 that is, not physically associated together but seen 

 near together only because lying nearly in the same 

 direction. The brighter star of a pair was in fact sup- 



1 It is, after all, at least as likely that Kahu assuming there really 

 was a planet known under this name might have been Vesta, the 

 brightest of the small planets which circle between Mars and Jupiter, 

 as the distant and slow-moving Uranus. For although Vesta is not 

 nearly so bright as Uranus, shining, indeed, only as a star of the 

 seventh magnitude, yet she can at times be seen without telescopic aid 

 by persons of extremely good sight ; and her movements are far more 

 rapid than those of Uranus. In the high table-lands of those eastern 

 countries, where some place the birth of astronomy, keen-sighted ob- 

 servers might quite readily have discovered her planetary nature, 

 whereas the slow movements of Uranus would probably have escaped 

 their notice. 



