178 ESSAYS ann OBSERVATIONS 
them ina level with the fables vented by 
the priefts of Egypt. According to feveral 
modern obfervations, the obliquity of the e- 
cliptic varies: but we are to remember, that 
even the noble Lycho Brache committed an 
error of 18’ in drawing his meridian in his 
ifland of Teraniburgum; and, from his errone- 
ous opinions concerning the refraction of the 
atmofphere, made the mean diftance of the 
moon lefs by 4 femidiameters of the earth 
than it really is. It is true, Mr Caffimi’s ob- 
fervation in 1655, compared with late ones, 
makes it vary at the rate of 55” in 79 years. 
Let us therefore fee, if a variation, fuch as 
that arifes from Meff. Caffini’s and Goden’s 
_obfervations, be not aconfequence of prin- 
ciples already eftablifhed in the folar fyftem ; 
and offer fome hints of a method by which 
it may be afcertained whether this be the juft 
folution of this queftion, and how, froma 
proper feries of obfervations, made with great 
exactnefs, an improvement and correCtion in 
geography and navigation may be deduced 
from this inquiry, by bringing the theory of 
the earth’s motion in her orbit, and particu- 
larly what relates to the declination of the 
fun to greater perfection. This will be the 
more 
