493 
Trigonometrical Survey. 
puted excess, one or two of the observed angles have appeared 
to have been determined with sufficient accuracy, as shown by 
the agreement of the angles obtained upon different parts of 
the arch ; the corrections for the chord angles have been added 
to, or taken from them, and the remaining angle or angles con- 
sidered as erroneous. In the case of one angle being supposed 
right, and the other two wrong, the errors have been consi- 
dered equal between the latter, unless the sum of the angles 
round the horizon at one of the stations, has indicated, that 
either the whole, or the greatest part of the excess or defect, 
was due to a particular angle. Likewise, when any triangle 
has been found in excess or defect, and all the angles have 
appeared to be determined with equal accuracy, the corrections 
for the reduction to the angles formed by the chords have 
been first applied, and then the errors considered equal. 
What is called the spherical excess in the fifth column, is 
computed according to the rule, page 171. Phil. Transac. Vol. 
LXXX. These excesses above 180° would, of course, be ex- 
actly the same as the respective sums of the differences in the 
fourth column, if both were not obtained from approximating 
rules. 
It is almost unnecessary to remark, that no computations 
have been attempted with the chords of the sides of the lesser 
triangles in the principal series. 
3 s 
MDCCXCVo 
