Ruskin, John; Cook, Edward T. [Hrsg.]: The works of John Ruskin: The elements of drawing. The elements of perspective. And the laws of Fésole (London, 1904)

RIGHT LINE BETWEEN GIVEN POINTS 255

COROLLARY I
If the line A B is in a plane parallel to that of the pic-
ture, one end of the line A B must be at the same direct
distance from the eye of the observer as the other.
Therefore, in that case, D T is equal to n' T.
Then the construction will be as in Fig. 7; and the

CCD


student will hnd experimentally that % 5 is now parallel
to A B.^
And that a 5 is to A B as T s is to T D.
Therefore, to draw any line in a plane parallel to that
of the picture, we have only to hx the position of one of
its extremities, % or 5, and then to draw from % or 5 a line
parallel to the given line, bearing the proportion to it that
T s bears to T n.
* For by the construction AT:aT::BT:6-r; and therefore the
two triangles A B T, a 5 T, (having a common angle A T B,) are similar.