[ 3 a 7 ] ' 
vation at Tobolfk, and an error of the fame quanti- 
ty in the obfervation at the Cape, and both in con- 
trary directions, this alfo will produce an error of 
only in the Sun’s parallax. If therefore no greater 
error could be committed in the obferyations at To- 
bollk and the Cape, we are certain that the compa- 
rifon of Tobolfk and the Cape gives the Sun’s paral- 
lax fo exaCt, that the error does not exceed one fe- 
cond from the true parallax. But this is too great an 
error to be fuppofed in the obfervations, becaufe I 
have fhewn, in my former paper, that an error of 
only 6 " in time was committed in the obfervation of 
the contaCt by perfons obferving even in the fame 
place ; therefore, if we fuppofe an error of 6 " of 
time in the obfervation at Tobollk, and an error 
of the fame quantity in the obfervation at the Cape, 
and both in contrary directions, the error produced 
in the parallax by thofe 1 2", will amount only to 4. 
of a fecond, even though we had only thefe two ob- 
fervations to determine the Sun’s parallax : But fince 
we have a great number of very good obfervations, 
made at other places, it follows that the mean of 
all thefe, muft give the Sun’s parallax to a lefs error 
than 4. of a fecond, and confequently very near the 
truth. 
In all places where the internal contaCt at the egrels 
was obferved, and where there were more obfervers 
than one, we find a difference in the time of each 
obferver ; the obfervation at Greenwich is an excep- 
tion to this, as the three obfervers all agree to the 
fame fecond, in the obfervation of the contaCt of 
Venus with the Sun’s limb ; which is the more fur- 
prizing as they ufed telefcopes of different conftruc- 
U u 2 tions 
