[ 3 26 ] 
If we fele<ft out of thefe 21 comparifons thofc 
places whofe difference of longitude may be fuppof- 
ed to be the bell determined, the mean of thefe may 
be regarded as the moft exaft determination, viz. 
Paris, Bologna, Greenwich, Savile-Houfe, Upfal, 
Stokolm, Cajaneburg and Tobolfk; the mean of 
thefe gives the Sun’s parallax rrr 8", 55, and if we 
leave out the refults of Greenwich and Tobolfk, 
which differ the mod from the reft, the mean of the 
remaining 6 refults gives it — 8", 56 the fame as 
before. 
The mean of the 21 comparifons with the obfer- 
vation at Rodrigues gives the Sun’s parallax — 8", 57, 
and if we rejedt 8 of them, which are marked with 
the letter r, and which differ more than Vr of a fe- 
cond from the mean of the whole, the mean of the 
remaining 13 refults gives the Sun’s parallax 8", 57, 
differing only one hundredth part of a fecond from 
that which was determined from the obfervation at 
the Cape, and agreeing in a moft furprizing manner 
with what was formerly determined by the compan- 
ions of the the obfervations at places on this fide of 
the Line only, where the bafe was fo fmall, as I faid 
before; a moft convincing proof of the great precifi- 
on with which the parallax of the Sun is determined 
by the late tranfit of Venus. 
We fhall now enquire into the limits of the error 
that may attend the determination of the parallax by 
the obfervation of the internal contact. An error of 
V io v of time in the obfervation at Tobolfk when 
compared with the obfervation at the Cape, will pro- 
duce an error of 1" in the Sun’s parallax : and 
if we fuppofe an error of 3 5" of time in the obfer- 
vation 
