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)

TO FIX THE POSITION OF A GIVEN POINT 258

of the observer, D c is to be measured to the right instead
of the left.
The figures 4 and 5, looked at in a mirror, will show
the construction of each, on that supposition.
Now read very carefully the examples and notes to this
problem in Appendix 1. (page 809). I have put them in
the Appendix in order to keep the sequence of following
problems more clearly traceable here in the text; but you
must read the first Appendix before going on.