[ 423 ] 
T . . - 
that time : whofe fluent, | k x — x co-fl E x Z — 
f iin. 2 Z, will eonfequently be the total regrefs of 
the point E, in the time that the fun, by his apparent 
motion, defcribes the arch HE or Z ; which, on the 
fun’s arrival at the folftice, becomes barely = l k x 
— x co-f. E x an arch of 90° : the quadruple where- 
T f 7 1 
of, or | k x — x co-f. E x 360° ( = x 
OA 1 — OP 2 
O A 2 
x co-f. E x 360°) is therefore the whole annual pre- 
eeflion of the equinox caufed by thej fun. This, 
in numbers (taking — \ comes out— ^ 
4 x 366^ 
X 
— - x 0.917176x3^0 = 21" 6 ". 
The very ingenious' M. Silvabelle, in his eflay on 
this fubjedt, inferted in the 48th volume of the Phi- 
lofophical Tranfadtions, makes the quantity of the an- 
nual preceflion of the equinox, caufed by the fun, to 
be the half, only, of what is here determined. But 
this gentleman appears to have fallen into a twofold 
miftake. Firft, in finding the momenta of rotation 
of the terreflrial fpheroid, and of a very {lender ring, 
at the equator thereof j which momenta he refers 
to an axis perpendicular to the plane of the fun’s 
declination, inftead of the proper axe of rotation, 
{landing at right angles to the plane of the equator. 
The difference, indeed, arifing from thence, with 
refpedt to the fpheroid (by reafon of its near approach 
to a fphere) will be inconfiderable ; but, in the ring, 
the cafe will be quite otherwife ; the equinodtial 
points thereof being made to recede juft twice as faff 
4 as 
