[ iS9 ] 
obfervation of thefe fmall angles principally depends 
upon the obfervation of the Sun’s right afcenfion. 
(which , depending on the meafure of time, is lefs 
capable of exaCt obfervation, than if depending on 
divided inftruments) ; the deductions thence drawn 
feem dill wanting of that certainty which the fubjeCt 
demands; and if to this we add, from a deduction 
of Mr. Mafkelyne, that the relative gravity of the 
Earth and Moon is as 76 to 1, derived from the effeCt 
that the Moon produces in the nutation of the Earth’s 
axis ; the relative gravity, and confequently the paral- 
laxes thereon depending, will be reduced to almoft 
one half of thofe refulting from Sir Ifaac’s determi- 
nation. 
It is true, that the quantity of effeCt of the men- 
ftrual parallaxes will not be great, if computed upon 
Mr. Malkelyne’s induction, for as much as that 
the common center of gravity will be confiderably 
within the Earth’s furface; yet* even in that cafe, the 
Sun’s tranlit over the meridian, when the Moon is in 
one quadrature, will differ nearly one fecond of time 
from that obferved in the oppofite quadrature ; and 
though De la Caille and Mayer have formed equations 
depending on the Moon* to be applied to the equation 
of time ; yet, if we are at an uncertainty, whether 
the maximum of this equation is one fecond, two 
thirds of a fecond, or half a fecond of time, each 
way, we are /till under a material difficulty ; for 
though thefe differences are fo fmall, that it is not' 
eafv to determine them exaCtly from folar obfervations ; 
yet, as they are capable of creating a fenfible diffe- 
rence in thefe obfervations, they will, fo long as they 
remain undetermined, prevent that folidity and firm- 
nefs 
