44 s dn Account of the Measurement 
method must be pursued. The necessity giving rise to this, 
originates from the radii of curvature of the oblique degrees con- 
tinually varying, and the angles of convergency, between the 
several sides and their respective meridians, remaining unknown. 
It must be remembered, that the sides of the several triangles 
projected over the country, in this Survey, are not to be consi- 
dered as so many distances on the earth’s surface, but the 
lengths of the chord lines subtended by arcs. Therefore, it is 
manifest that, strictly speaking, all the chord angles should be 
used, and not the horizontal ones ; with which, after the bearing 
of the first side with the meridian has been reduced to some 
plane beneath the earth’s surface, a number of chord lines in 
the plane of that meridian are to be computed ; the sum of which, 
augmented by the differences between those chords and their 
respective arcs, will give the true meridional distance. I have 
been at the trouble to calculate the distance between Clifton and 
Dunnose on this principle ; and find the length of my arc to be 
1036339,5 feet ; which is, about 2^ feet more than the distance 
determined by the other mode of computation. An advantage, 
however, attending a calculation on the principle now spoken 
of, is the ability of calculating, pretty nearly, the azimuth of any 
one station from an extremity of the arc. This, if the instru- 
ment with which the direction of the meridian is observed be 
not well divided, or otherwise not exactly fit for the operation, 
is necessary, and should be always done. The angle at Clifton, 
between Gringley on the Hill and the meridian, was observed 
to be 76° 17' 25". According to my computation in the way 
spoken of, that angle is 76 if 30". A difference of 5", working 
a 1 the way up from Dunnose through an arc of 2 0 50', is as 
small as can be expected, and serves to prove that the angles of 
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