Note Footnote 14 — PROBLEM III.

: The student will observe, in practice, that, his paper lying flat on the table, he has only to draw the line T V on its horizontal surface, parallel to the given horizontal line A B. In theory, the paper should be vertical, but the station-line S T horizontal (see its definition above, page 5); in which case T V, being drawn parallel to A B, will be horizontal also, and still cut the sight-line in V.