ion to the heights. I have
left these lines on the drawing, and also different parts of it
unfinished, so as to show the different stages of the work. These guide
lines are done mentally later on, when the student is more advanced, and
with more accuracy than the clumsy knitting-needle. But before the
habit of having constantly in mind a vertical and horizontal line with
which to compare positions is acquired, they should be put in with as
much accuracy as measuring can give.

[Sidenote: Blocking in your Drawing.]

The next thing to do is to block out the spaces corresponding to those
occupied by the model in the field of your vision. The method employed
to do this is somewhat similar to that adopted by a surveyor in drawing
the plan of a field. Assuming he had an irregular shaped one, such as is
drawn in Fig. X, page 87 [Transcribers Note: Diagram IV], he would
proceed to invest it with straight lines, taking advantage of any
straightness in the boundary, noting the length and the angles at which
these straight lines cut each other, and then reproducing them to scale
on his plan. Once having got this scaffolding accurately placed, he can
draw the irregularities of the shape in relation to these lines with
some certainty of getting them right.

You should proceed in very much the same way to block out the spaces
that the forms of your drawing are to occupy. I have produced these
blocking-out lines beyond what was necessary in the accompanying drawing
(page 87 [Transcribers Note: Diagram IV]), in order to show them more
clearly.

[Sidenote: How to observe the Shape of Curves.]

There is yet another method of construction useful in noting accurately
the shape of a curved line, which is illustrated in Fig. Y, page 87
[Transcribers Note: Diagram IV]. First of all, fix the positions of the
extremities of the line by means of the vertical and horizontal. And
also, as this is a double curve, the point at which the curvature
changes from one direction to the other: point C. By drawing lines CA,
CB and noting the distances your curves travel from these straight
lines, and particularly the relative position of the farthest points
reached, their curvature can be accurately observed and copied. In
noting the varying curvature of forms, this construction should always
be in your mind to enable you to observe them accurately. First note the
points at which the curvature begins and ends, and then the distances it
travels from a