Indian Science and Technology in the Eighteenth Century: Some Contemporary European Accounts c9.43

c9.43

26. But, to return to what respects the moon's acceleration; it is plain, that tables, as ancient as those of Tirvalore pretend to be, ought to make the mean motion of that planet much slower than it is at present. They do accordingly suppose, in the rule for computing the place of the moon, already described, that her motion for 4383 years, 94 days, reckoned in the moveable Zodiac from the epoch of the Calyougham, is 7s, 2°, 0′, 7″, or 9s, 7°, 45′, 1″, when referred to the fixed point of the vernal equinox. Now, the mean motion for the same interval, taken from the tables of Mayer, is greater than this, by 2°, 42′, 4″,41 which, though conformable, in general, to the notion of the moon's motion having been accelerated, falls, it must be confessed, greatly short of the quantity which Mayer has assigned to that acceleration. This, however, is not true of all the tables; for the moon's motion in 4383 years, 94 days, taken from those of Chrisnabouram, is 3°, 2′, 10″ less than in the tables of Tirvalore;42 from which it is reasonable to conclude, with M. Bailly, that the former are, in reality, more ancient than the latter, though they do not profess to be so: and hence, also, the tables of Chrisnabouram make the moon's motion less than Mayer's, for the above mentioned interval, by 5°, 44', 14", which therefore is, according to them, the quantity of the acceleration.