ASTRONOMY of the BRAHMINS. 161 



tion, be fubject to change, it will, after a certain interval, re- 

 turn to the fame ftate in which it is at prefent, and leave no 

 room for the introduction of diforder, or of any irregularity 

 that might conftantly increafe. Many of thefe periods, how- 

 ever, are of vaft duration. A great number of ages, for in- 

 flance, rauft elapfe before the year be again exactly of the 

 fame length, or the fun's equation of the fame magnitude as at 

 prefent *. An aftronomy, therefore, which profeffes to be fo 

 ancient as the Indian, ought to differ confiderably from ours in 

 many of its elements. If indeed thefe differences are irregular, 

 they are the effects of chance, and muft be accounted errors ; 

 but if they obferve the laws, which theory informs us that the 

 variations in our fyftem do actually obferve, they muft be held 

 as the moft undoubted marks of authenticity. We are to ex- 

 amine, as M. Bailly has done, which of thefe takes place in 

 the cafe before us f . 



30. The tables of Tirvalore, which, as we have feen, refer 

 their date to the beginning of the Calyougham, make the fy- 

 derial year to confift of 365^, 6 b , 12', 30"; and therefore the 

 tropical of 365^, 5 b , 50', 2,5 > which is 1', 46", longer than 

 that of De la Caille %. Now, the tropical year was in rea- 

 lity longer at that time than it is at prefent ; for though the fi- 

 derial year, or the time which the earth takes to return from 

 one point of fpace to the fame point again, is always of the 

 fame magnitude, yet the tropical year being affected by the 

 precefhon of the equinoxes, is variable by a fmall quantity, 

 which never can exceed 3', 40", and which is fubject to flow, 

 and unequal alternations of diminution and increafe. A the- 

 orem, expreffing the law and the quantity of , this variation, has 

 been inveftigated by M. de la Grange, in the excellent Me- 

 Vol. II. x moir 



* Mem. de PAcad. de Berlin, 1782, p. 170, &c. 

 f Aft. Ind. p. 160, &c. 

 J Supra, § 18. and 10. 



