measure, this may be done by large drawing-pins.
If, however, a large tube or thick sheet of glass is to be graduated,
fix it in position by two strips of wood screwed to the table on each
side of it. One of these wooden strips, on which the measure may be
placed, may be about as broad as the standard measure, and of such
thickness that when the measure lies upon it beside the tube to be
graduated, the ruler, when moved along the measure, will move freely
above the tube, but will not be elevated more than is necessary to
secure free movement. The second strip of wood may be narrower, and of
the same thickness as the broader piece on which the standard measure
rests. In any case, let the standard measure and the object to be
graduated be very firmly secured in their places. Bring the ruler into
position at any desired part of the tube by placing the points of the
screws (_GG_) in corresponding divisions of the scales (_AA_). With the
style, which may be a needle mounted in a handle, make a scratch in the
wax along the edge of the ruler at _F_, move the ruler so that the
screws rest in the next divisions, and repeat the operation till the
required number of lines has been ruled. Longer marks may be made at
intervals of five and ten millimetres. Great care must be taken to hold
the needle perpendicularly, and to press it steadily against the edge
(_LL_) of the ruler in scratching the divisions.[19] The length of the
lines marking the millimetre divisions should not be too long; about 1
mm. is a good length. If they are longer than this, the _apparent_
distance between them is diminished, and it is less easy to read
fractions of millimetres. Before removing the scale to etch the glass,
carefully examine it to see that no mistakes have been made. If it is
found that any lines have been omitted, or that long lines have been
scratched in the place of short ones, remelt the wax by means of a
heated wire, and make new marks. Finally, mark the numbers on the scale
with a needle-point, or better, with a fine steel pen.

[19] To avoid variations of the position in which the needle is held
when marking the divisions, the edge (_LL_) should not be bevelled; and
an upright support may be placed upon the ruler, with a ring through
which the handle of the needle passes, thereby securing that the angle
formed by the needle and surface of the ruler is constant, and that
equal divisions are marked.

The marks on the wax should cut through