Join E D, and produce it to cut the sight-line in V′.
Fig. 72.
[p96]
]Then, since the point E is vertically under the point B, the horizontal line E D is vertically under the inclined line B D.
Fig. 73.
So that if we now let fall the vertical V′ P from V′, and produce B D to cut V′ P in P, the point P will be the vanishing-point of B D, and of all lines parallel to it.[Footnote 35] ]
[Footnote 34: ] The diagram is inaccurately cut. Y V should be a right line.] [Return to text]
[Footnote 35:] The student may perhaps understand this construction better by completing the rectangle A D F E, drawing D F to the vanishing-point of A E, and E F to V. The whole figure, B F, may then be conceived as representing half the gable roof of a house, A F the rectangle of its base, and A C the rectangle of its sloping side.