[ 3 ^' 3 
what thofe Correftions were, that wc may fee whe-. 
ther they were realJy neceflary or no? Why were: 
they not taken notice of in the Calculations of each 
Triangle ? Befides, the real Length of the Bafe, or the 
fundamental Line, in Rouffillon^ is not fully afcer> 
tained, it not being meafured more than once j whereas- 
that at ’Dunkirk and that of Mr. Ticard were mea- 
fured twice j and there was more Reafon for doing 
fo here than at Dunkirky on account of the uneven 
and almoft ever changing Shore in RouffilloUt from 
the reftlefs overflowing Sea. 
The great Number of the Triangles, joined with 
the numerous fmall Errors of the Angles, is another 
Ground of Uncertainty j for the Errors in the Angles, 
though fmall, may make the Diftance of the Parallels 
of the Two extreme Places greater than it ought to 
be } and yet the principal Sides, that is, thofe that are 
madeBafes to the following Triangles, continue the 
fame. This made it neceffary to verify the Sides, at 
leaft at every fecond Degree, by meafuring the prin- 
cipal Bafe twice over with due Care j which might 
have been done, and therefore fhould have been 
done, in a Matter of fo much Nicety as an Attempt 
to find the Difference between Two Degrees fo near 
one another, under the fame Meridian. 
To fhew what bad Confequences may arife from 
fmall Errors committed in obferving the Angles of 
feveral Triangles, Mr. Olavus Hiorter, a curious and 
ingenious Friend of Mr. CelfiuSy has taken the Pains 
to form the Triangles of Mr. CaJJini between Bourges 
and CoUiourey fo that the Diftance between their 
Parallels (hall be confiderably leflened 5 and yet the 
Bafe in RouJJlllony found by Computation, (hall not, 
after due Correction, differ fenfibly, if at all, from 
C c c 2 the 
