2 



Remarks on Booh 11. Chapter 2 



[No. 39, 



which, amid certain astronomical details, affords a clue to the lati- 

 tude of the writer, a point, as it seems to us, of no little interest. 



The following is an extract from the eighth chapter. 



" As the circumference of a potter's wheel revolves most rapidly, 

 so the sun travels rapidly on his southern journey : he flies along his 

 path with the velocity of wind, and traverses a great distance in a short 

 time. In twelve muhurttas he passes through thirteen lunar aste- 

 risms and a half during the day ; and during the night he passes 

 through the same distance only in eighteen muhurttas. As the 

 centre of the potter's wheel revolves more slowly than the circum- 

 ference, so the sun in his northern path again revolves with less ra- 

 pidity and moves over a less space of the earth in a longer time, 

 until, at the end of his northern route, the day is again eighteen 

 muhurttas, and the night twelve ; the sun passing through half the 

 lunar mansions by day and by night in those periods respectively. 5 ' 



Now since a muhurtta is forty- eight minutes of time, or twelve 

 degrees, it follows that the hour- angle from sunrise to noon on the 

 longest day was equal to one hundred and eight degrees. Assuming 

 the obliquity of the ecliptic to have been twenty-three and a half 

 degrees, and omitting for the present all consideration of refraction, 

 we obtain the following results from the solution of the well known 

 quadrantal triangle Z P S, where Z is the zenith of the observer, P 

 the north pole, and S the sun at rising, 

 sine (Z P S— 90 ° )=cotan Z P. co- 

 tan PS, or, 1 being the latitude of Z, Z 



tan 1 = sine 18°. cotan23|.° 'NT^^^. 



Hence the latitude is 35° 24' p 

 approximately. This value of the \ 1 



latitude however involves the as- \ / 



sumption that refraction was al- \ / Fig. 1, 



lowed for by the writer, which \ / 



cannot well have been the case ; \ / 



it is therefore necessary to find y 

 the effect of refraction on the 

 longest day. 



