the Trigonometrical Operation. z g 
In order to complete the triangular connection between 
Greenwich and Paris, there remains yet one triangle more (the 
XLVth) to be given, whereby we fhall be enabled to connect 
the point M near Dunkirk with Dover. For this purpofe it is 
neceflary to make fome remarks on the Dunkirk bafe ; and 
alfo to ihew, from the French operations, how the point M is 
fituated with refpeCt to Paris, Dunkirk, and Calais. 
M . Cassini de T. hury, in his book already quoted (p. 22. and 
54.) has informed us of the manner in which this bafe on the 
Strand near Dunkirk was meafured ; and that its mean length 
amounted to 6224.36 toifes, which are equal to 39801.7 Eng- 
liih feet. Thus it appears, that there is a difference as above 
ftated of feven feet in defeCt, between the meafured and com- 
puted length of the laft fide of a combined feries of 44 Britifh 
and French triangles, depending on a bafe meafured on Houn- 
flow Heath, and verified by another meafured in Romney 
Marfli. But a feries of 24 French triangles, founded on a 
bafe meafured near Paris, and corrected by another executed 
near Amiens, gives for the length of the fame bafe near Dun- 
kirk 39809.94 Englifh feet, and confequently only an excefs of 
15 inches with regard to our refult. This very near agree- 
ment in the determination of the fame length by two different 
ieriefes of triangles, whofe extremities are fituated at fo great a 
difiance from each other, fufficiently proves the excellency of 
trigonometrical meafurement, and fhews to what a wonderful 
degree of accuracy operations of this fort may be brought 
when fine inftruments are made ufe of, and great care bellowed 
in the application of them. Doubtlefs fmall errors may have 
arilen in the progrefs of the work, unfeen on both fides ; but 
thefe falling fometimes one way and fometimes the other, they 
feem fo far to have compenfated for, or deftroyed each other, 
3 that 
