﻿262 ON THE ASTRONOMICAL COMPUTATIONS 



himself of the methods used by European astrono^ 

 meisto determine the moon's horizontal parallax. la 

 general terms, it is to observe the moon's altitude, 

 and thence, with other requisites, to compute the time 

 of her ascension from the sensible cshit'ija, or horizon, 

 and her distance from the sun when upon the rational 

 horizon, by which to find the time of her passage from 

 the one point to the other ; or, in other words, * to 

 « find the difference in time between the meridian to 

 « which the eye referred her at rising, and the meridian 

 * she was actually upon ;' in which difference of time 

 she will have passed through a space equal to the earth's 

 semidiameter or 800 Yojan : and by proportion, as that 

 time is to her periodical month, so is 800 Yojan to the 

 circumference of her cacsha, 324000 Yojan. The errors 

 arising from refraction, 'and their taking the moon's 

 motion as along the sine instead of its arc, may here be 

 remarked ; but it does not seem that they had any 

 idea of the first *, and the latter they perhaps thought 

 too inconsiderable to be noticed.: Hence it appears 

 that they made the horizontal parallax 53' 20" and her 

 distance from the earth's centre 5T570 Yojan; for 



i8o°V 1600 i ir j o / • ..i j" 



- — =s= c 2 20 : and as 00 or caoo is to the radius 



32AOCO J J s *>* 



3438', fo is one -fourth of her orbit 81000 Yojan to 



dCTv-OX 2I6O0 Ol V 



- — == 220184, tne same distance 



in geographical miles. European astronomers com- 

 pute the mean distance of the moon about 240000, 

 which is something above a fifteenth part more than 

 the Mndvs found it so long ago as the time of Meya 9 

 the author of the Surya Siddhanta* 



By the Hindu system the planets are supposed to 

 move in their respective orbits at the same rate - t the. 

 dimensions therefore of the moon's orbit beings 



* But they are not wholly ignorant of optics : they know the 

 angles of incidence and reflection to be equal, and compute the 

 place of a star or planet, as it would b« seen reflected from water 

 or a minor. 



