Enlarging and Reducing
When drawings are enlarged or reduced, the linear dimensions and not those of the area are implied; thus one half means one half of both width and height—really one-fourth of the area. It is obvious that half the area would be a different proportion, and it is the proportion that is concerned.
No. 286. Diagonal Method of Enlarging or Reducing. Solid line shews given size.
Divisional measurement is rendered unnecessary by the diagonal method of proportion. Given a rectangular shape, which has to be reduced or enlarged, a diagonal line should be drawn, and prolonged if the latter, through opposite angles. A line parallel to either the vertical or horizontal can be drawn and returned at a right angle where it intersects the diagonal, and regardless of any dimensions, this will ensure the exact proportion of the original rectangle.
It is obvious that such designs as the foregoing should be complete, and both in drawing and colour a perfect anticipation of the painted result, owing nothing of their effect to mechanical reproduction.