The Elements of Perspective / arranged for the use of schools and intended to be read in connection with the first three books of Euclid

by John Ruskin

[Footnote 17: ] The demonstration is in Appendix II. Article II. [p. 101.]] [Return to text]

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][PROBLEM IV.]

TO FIND THE DIVIDING-POINTS OF A GIVEN HORIZONTAL LINE.

Fig. 15.

Let the horizontal line A B ([Fig. 15.]) be given in position and magnitude. It is required to find its dividing-points.

Find the vanishing-point V of the line A B.

With center V and distance V T, describe circle cutting the sight-line in M and N.

Then M and N are the dividing-points required.

In general, only one dividing-point is needed for use with any vanishing-point, namely, the one nearest S (in this case the point M). But its opposite N, or both, may be needed under certain circumstances.