7i2 Mr. hutton’s Calculations to afcertain 
great labour and pains, I had frequently the mortifica- 
tion to find that the feveral values of the fame lines 
would differ fo greatly one from another, that I was 
often very doubtful whether I could rely on any of them, 
or even on the mean among them all, Thefe differences 
arofe from the fmall errors in the obferved angles, which 
in fome degree are unavoidable; and indeed they were 
fo fmall, that the fum of the angles of the feveral tri- 
angles which were ufed in the calculation feldom dif- 
fered by more than a minute or two from 1 8o°. But in 
a long connected chain of triangles, dependant on one 
another, the effects of fuch fmall errors at length be- 
come too great to be tolerated in a computation requiring 
much accuracy. Another method is, fir ft to compute 
.from both bafes the length of the line kn extended along 
the ridge of the hill from Eaft to Weft, and from it, as a 
fecondary bafe, compute all the other lines in the plan. 
This method admits of much more accuracy than the 
former, fuppofing this fecondary bafe to be truly af- 
figned; becaufe that, from the elevated and central filia- 
tion of this line, all or moft of the other points in the 
furvey are vifible from one or both of its extremities, by 
which it happens that the other lines are moftly deter- 
minable from it alone, without fo clofe a connection with 
one another as in the other method of computation. By 
both 
