propofed trigonometrical Operation . 193 
as good an interfe&ion of the lad as we are certain of getting of 
the two fird ; but the breadth of the range of chalk hills 
being little different on our fide from what it is on theirs, 
by confining ourfelves to fuch a bafe as they will afford us, we 
cannot any way obtain an interfered angle at Calais greater 
than about 29 0 or 30°. 
Thinking that poflibly from St. Peter’s church in the ide of 
Thanet the tower of Notre Dame at Calais may be feen, I have 
extended dotted triangles into that part of Kent ; becaufe, if 
the united heights fhould not be diffident to raife the top of 
the tower above the curvature of the fea, which is the only 
thing to be doubted, we are always certain, that the fignal of 
Blancnez may, by means of the Indian lights, be eafily feen, 
fmce the whole range of chalk hills behind Calais are dis- 
covered with the naked eye from the ide of Thanet, when the 
weather is tolerably clear. 
Having in this manner afeertained the relative dtuations, 
with regard to the coad of England, of three points on the 
coad of France, forming a triangle whofe ddes and angles 
we already know from their trigonometrical operations, we 
lhall in like manner be enabled to determine the fituation of 
the point M near Dunkirk, where the meridian of the Royal 
Obfervatory of Paris interfe&s a line drawn from the great 
tower of Dunkirk to that of N. D. at Calais. (See Tab. IX.) 
The didance MP, on the meridian of Paris, will then be had ; 
and that being added to 13341 7 fathoms, the didance of INI 
northward from the Royal Obfervatory, we (hall have the total 
terredrial arc, comprehended between the parallels of the two 
Obfervatories, anfwering to an arc in the heavens of 2 0 38' 
26", or a difference cf latitude between 5-1° 28' 40" and 
48° 50' 1 4 // . 
Vol. LXXVIL C c hi 
