836 Description of an Astronomical Instrument. QOct. 



omission of certain elements which the European astronomer takes 

 into account. But little familiarity with astronomy is necessary to 

 an apprehension of the fact that, whatever apparently elevates the 

 sun above his true position must, in the same ratio, diminish the 

 shadow of the gnomon, and consequently the latitude thence de- 

 duced. Now refraction does this to a small extent, and the rays of 

 light from the sun's upper limb cause a much greater error of the same 

 kind. 



Making the necessary corrections, we have 



Difference, .. .. — 34' 16" 



Refraction, -f 26" 



Sun's semidiameter, .. ..-J-16' 4" 



True difference, .. — 17' 46" 



This is, as I doubt not will be generally allowed, a difference 

 astonishingly small, considering the imperfection of the instrument 

 employed in observation. 



Before entering on the examination of the Table of Ascensions of the 

 Signs as given above, it may be as well to inform the reader that 

 after having ascertained the occurrence of any celestial phenome- 

 non, such as an eclipse for instance, in sideral time, the astronomer 

 next converts this into civil time ; to do which it is necessary that he 

 should know how long each sign occupies in rising. This he effects 

 in the following manner : — 



Let us take for example the sign Aries, the place Khota, the length 

 of the equinoxial shadow, as it is given to us, 5 ungols and 30 beun- 

 gols, and the obliquity of the ecliptic 24° 



1 : Sin 24 : : Sin 30 : Sin decl. 

 9-6093133 

 9 6989700 



93082833 



12 : 5 5 : : Sin decl. : Chitija 



89207188 

 07603627 

 97082833 



8-9693648 



