The simplest and most mechanical way of observing things as a flat subject is to have a piece of cardboard with a rectangular hole cut out of the middle, and also pieces of cotton threaded through it in such a manner that they make a pattern of squares across the opening, as in the accompanying sketch.  To make such a frame, get a piece of stiff cardboard, about 12 inches by 9 inches, and cut a rectangular hole in the centre, 7 inches by 5 inches, as in Diagram III.  Now mark off the inches on all sides of the opening, and taking some black thread, pass it through the point A with a needle (fixing the end at this point with sealing-wax), and across the opening to the corresponding point on the opposite side.  Take it along to the next point, as shown by the dotted line, and pass it through and across the opening again, and so on, until B is reached, when the thread should be held by some sealing-wax quite taut everywhere.  Do the same for the other side.  This frame should be held between the eye and the object to be drawn (one eye being closed) in a perfectly vertical position, and with the rectangular sides of the opening vertical and horizontal.  The object can then be observed as a flat copy.  The trellis of cotton will greatly help the student in seeing the subject to be drawn in two dimensions, and this is the first technical difficulty the young draughtsman has to overcome.  It is useful also in training the eye to see the proportions of different parts one to another, the squares of equal size giving one a unit of measurement by which all parts can be scaled.

[Illustration:  Diagram III.

A device for enabling students to observe appearances as A flat subject]

[Sidenote:  Fixing Positions of Salient Points]

Vertical and horizontal lines are also of the utmost importance in that first consideration for setting out a drawing, namely the fixing of salient points, and getting their relative Positions.  Fig.  Z, on page 87 [Transcribers Note:  Diagram IV], will illustrate what is meant.  Let A B C D E be assumed to be points of some importance in an object you wish to draw.  Unaided, the placing of these points would be a matter of considerable difficulty.  But if you assume a vertical line drawn from A, the positions of B, C, D, and E can be observed in relation to it by noting the height and length of horizontal lines drawn from them to this vertical line.  This vertical can be drawn by holding a plumb line at arm’s length (closing one eye, of course) and bringing it to a position where it will cover the point A on your subject.  The position of the other points on either side of this vertical line can then be observed.  Or a knitting-needle can be held vertically before you at arm’s length, giving you a line passing through point A. The advantage of the needle is that comparative measurements can be taken with it.