220 
Gen . Roy’s Account of 
Art. XI. Comparifon of the angle between the meridian of 
the point M and a line drawn from thence to Calais, as 
approximately deduced from the Brit if and French obfer - 
various. 
In the fpneroidical quadrilateral GgrM (fig. 8.), formed by 
three arcs of three great circles, and one of a fmall circle of the 
fpheroid, we have two right angles at G and r, and two others 
at g and M, each greater than a right angle by 5G.7 ; there- 
fore the angle RMC, refuiting from the triangles = 14 5 d 
— RMr (1 p /7 .4 2 ) ~ 1 4 ° 5° 7 44 "-S+ 9 °° q/ 9 "'7 ( CM <?) = 
104° 50' 54 y/ .*2, is the angle ^MC, or that which Calais makes 
with a parallel to the meridian of Greenwich drawn through 
the --point M. From this laft angle fubtradting the angle PM g 
= i° 48' 38G6, or the quantity by which the meridian of M 
(fuppofed to co incide with that of Paris) converges towards 
that of Greenwich, there remains the angle PMC =103 2 7 
ic".6 for the angle that the meridian of M fhould make with 
a line drawn from D, or Dunkirk, through that point to Ca- 
lais, according to the Britifh obfervations. 
By the late French operations, the meridian of Dunkirk 
makes, with a line drawn through M to Calais, an angle of 
102 0 59 7 51 // «5'. The convergence of the meridian of M to 
that of Dunkirk, on a difference of longitude of 2 / 21^.54, 
is l 7 49 /7 .94, which being added to 102° 59' 51 7/ .-5, we have 
1 03° i 7 4i // .44 for the angle that the meridian of M, or of 
Paris, makes with a line drawn from Dunkirk through that 
point to Calais. The difference between the two refults 34 7 / .i6 
is nearly equal to the mean of two extremes f — -g ) = 37" is 
the apparent uncertainty, in the determination of that angle 
is by 
