ASTRONOMY of the BRAHMINS. t6i 



tion, be fubjedl 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 introdudlion of diforder, or of any irregularity 

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

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

 ftance, muft elapfe before the year be again exadly of the 

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

 prefent *. An aftronomy, therefore, which profefTes 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 effecls of chance, and muft be accounted errors ; 

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

 variations in our fyftem do adlually 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*, 1 2', 30" ; and therefore the 

 tropical of 365'', 5*, 50', 2,5"t which is i', 46", longer than 

 that of De la Caille f. 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 fronx 

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

 fame magnitude, yet the tropical year being affected by the 

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

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

 and unequal alternations of diminution and increafe. A the- 

 orem, expreffmg the law and the quantity ofthis variation, has 

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



VoL. II. X moir 



» Mem. de I'Acad. de Berlin, 1782, p. 170, &c. 

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

 i Supra, § 18. and 10. 



