80 Wright’s Mathematical Papers. 
nated by N, placed before the corresponding angle of commutation ; 
and likewise place, or suppose to be placed, N, or the negative sign, 
before the bases, whose positions are denoted by N, after the corres- 
ponding angle of commutation. : 
Make the factor in the third column, corresponding to the second 
side, equal to 0, and let the perpendicular belonging to the second 
be considered as the first factum resulting from the perpendiculars. 
Then perform the following operation, for each of the remaining 
sides. When its perpendicular and the next preceding factum have 
values of the same kind, take their sum, prefixing the negative sign 
when they are negative; but when they have values of different 
kinds, take their difference, placing the negative sign before it, when 
the greater number is negative. Then the factum thus obtained, 
and the base belonging to the side, will be factors, to be multiplied 
together. Again, observing the foregoing directions, take the sum, 
or difference, as the case may be, of the perpendicular and factum 
last obtained. Bring the several products, whose factors are AA or 
NN, into one sum, and the several products, whose factors are AN 
or NA, into another sum. Take the difference of these sums, half 
of which will be the required area of the polygon. 
Example 1. The same as in No. I. 
