,
c d
, etc., approach the point V, the smaller they become; and, whatever lengths may be added to the line A D, and successively cut off from
a
V, the line
a
V will never be cut off entirely, but the portions cut off will become infinitely small, and apparently “vanish” as they approach the point V; hence this point is called the “vanishing” point.
[p26]
][COROLLARY II.]
It is evident that if the line A D had been given originally, and we had been required to draw it, and divide it into three equal parts, we should have had only to divide its sight-magnitude,
a d′