744 PHILOSOPHICAL TRANSACTIONS. [aNNO l/QO. 



of Bikramajit, the era of SalaMn, the Bengal era, not strictly Hindoo, and the 

 cycle of 60 years. 



Before proceeding to a comparison of their several dates, it will be proper to 

 define the nature of the year and its constituent parts, according to which these 

 eras are computed by the Brahmans, who are the depositaries of science as well 

 as of religion. Their astronomical year is the measure of that portion of time 

 which is employed in a revolution of the sun, from the moment of his departure 

 from a certain star in their zodiac, as seen from the earth, till his return to the 

 same. It is therefore solar and sidereal, and contains, by their calculation, S^S** 

 gh J 2"" 30®; and as they suppose the annual movement of the stars in longitude, 

 or the precession of the equinoxes, to be 54", or 21"* 36® of time (admitting 

 with them, the sun to move at the rate of a degree each day), their tropical year 

 will be 365^^ 5*^ 50"* 54®: but as the sun really moves over 54" in 21"* 55% its 

 length is strictly 365^^ 5^ 50"* 35% or 1"* 52® greater than the tropical year as 

 determined by Mayer at 365^^ 5^ 48"* 43®. The true precession being 50".3, 

 which space the sun describes in 20"* 25®, the true sydereal year is 365^^ 6^ 9"* 8*, 

 and consequently the Hindoo year exceeds it by 3"* 22®, or I day in 430 years. 

 If the opinion of astronomers is well founded, that a sensible diminution in the 

 length of the year, as well as in the angle of obliquity of the ecliptic, has gra- 

 dually taken place in the lapse of many ages, it will follow, that this error may 

 not have existed, or been so great, at the period of adjusting the Hindoo tables: 

 and when we consider that there appears no ground to believe their apparatus for 

 observing was ever much superior to what it is discovered among the Brahmans 

 of this day, we are led to wonder at the precision attained to in this determina- 

 tion, and which, in the calculation of the moon's apogee, is still more remark- 

 able. The defect of art can have been compensated only by the remote antiquity 

 in which the series of their observations originated, affording an opportunity of 

 correcting the inaccuracy of particular measurements by a mean of large numbers 

 and distant intervals. 



They divide the zodiac into 28 lunar, and into ]2 solar constellations or signs, 

 and their astronomical year commences with the sun's arriving at the first point 

 of their constellation of Aries. This division of the zodiac, so far as the accu- 

 racy of their observations allows, is connected with the actual phenomena of the 

 heavens, and advances with the apparent motion of the stars, from east to west, 

 leaving gradually behind it the equinoctial points, and is not, like our zodiac, 

 an abstract division of space, attached to those points, and independent of the 

 starry system. Calculating on their principles, the difference of the 2 zodiacs, 

 or the accumulated amount of the annual precession, since the coincidence sup- 

 posed to be in the year of the Christian era 499, is in the present year 19° 21' 54". 



The length of their months is determined by the time which the sun employs 



