much
matter as to its precise location on the board, but otherwise it is best
to place it as near the left-hand edge of the board as convenient, as is
shown in Figure 14.

The lower edge, D, Figure 15, of the paper, however, should not be
placed too near the edge, A, of the board, because if the end P of the
square back comes down below the edge of the board, it is more difficult
to keep the square back true against the end of the board.

The paper must lie flat upon and close to the surface of the board, and
a sufficient number of tacks must be used to effect this purpose.

Drawings that are to be intricate, or to contain a great many lines, as
a drawing of an engine or of a machine, are best pasted or glued all
around the edges of the paper, which should first be dampened; but as
the learner will scarcely require to make such drawings until he is
somewhat familiar with and well practised in the use of the instruments,
this part of the subject need not be treated here.

TRACING PAPER.

For taking tracings from drawings tracing paper or tracing cloth is
used. They require to be stretched tightly and without wrinkles upon the
drawing. To effect this object the mucilage should be thick, and the
tracing paper should be dampened with a sponge after it is pasted. It
must be thoroughly dry before use, or the ink will run.

Tracing cloth must be fastened by pins or thumb tacks, and not dampened.
The drawing should be made on the polished side of the cloth, and any
coloring to be done should be on the other side, and done after the
tracing is removed from the drawing.

THE INK.

India ink should always be used for mechanical drawing: First, because
it lies upon and does not sink into the paper, and is, therefore, easily
erased; and, secondly, because it does not corrode or injure the drawing
instruments.

India ink is prepared in two forms--in the stick and in a liquid form.
The stick ink is mixed in what are termed saucers, or cabinet saucers,
one being placed above the other, so as to exclude the dust from
settling in it, and also to prevent the rapid evaporation to which it is
subject.

The surface of the saucer should be smooth, as any roughness grinds the
ink too coarsely, whereas the finer it is ground or mixed the easier it
will flow, the less liability to clog the instruments, and the smoother
and more flat it will lie upon the paper. In mixing the ink only a small
quantity of water should be used, the