against one of the two edges, holding it fast with the left hand; then move the triangle A along the edge of B. The edge a b will be parallel to the line c d; and when the edge a b reaches the point g, through which it is desired to draw the parallel line, hold both triangles stationary with the left
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hand, and draw the line e f by passing the pencil along the edge a b. Should the triangle A extend too far beyond the edge of the triangle B after a number of lines have been drawn, hold A stationary with the left hand and shift B along the edge of A with the right hand, and then proceed as before.
5. A line may be drawn at right angles to another line which is neither vertical nor horizontal, as illustrated in Fig, 7. Let c d be the given line (shown at the left-hand side). Place one of the shorter edges, as a b, of the triangle B so that it will coincide with the line c d then, keeping the triangle in this position, place the triangle A so that its long edge will come against the long edge of B. Now, holding A securely in place with the left hand, slide B along the edge of A with the right hand, when the lines h i, m n, etc. may be drawn perpendicular to c d along the edge bf of the triangle B. The dotted lines show the position of the triangle B when moved along the edge of A.
