lens. A
tool thus made is very convenient, accurate, and good, but it is
difficult to keep it in shape for any length of time; if left on the
lens it is apt to stick, and if it overhangs ever so little will, of
course, droop at the edges.

On the whole, the following will be found a good and sufficient plan.
The glass-grinding tool is converted into a polishing tool by pasting
a bit of thin paper over its surface; a bit of woven letter paper of
medium thickness with a smooth but not glazed surface does very well.
We have found that what is called Smith's "21 lbs. Vellum Wove" is
excellent. This is steeped in water till quite pliable and almost
free from size. The glass tool is brushed over with a little thin
arrowroot or starch paste, and the paper is laid upon it and squeezed
down on the glass squares as well as possible; if the paper is wet
enough and of the proper quality it will expand sufficiently to
envelop the tool without creases, unless the curvature is quite out of
the common.

This being accomplished, and the excess of water and paste removed,
the face of the paper is (for security) washed with a little clean
water and a bit of sponge, and, finally, the tool is slightly pressed
on the lens so as to get the paper to take up the proper figure as
nearly as possible. After the polishing tool has been thus brought to
the proper figure, it is lifted off and allowed to dry slowly. When
the paper is dry it may be trimmed round the edges so as not to
project sensibly beyond the glass squares. The next step is to brush
the surface over very carefully with polishing rouge (prepared as is
described at the end of this section) by means of a hat-brush. When
the surface of the paper is filled with rouge all excess must be
removed by vigorous brushing.

Fig. 53.

The tool being placed on the lens, two or three strokes similar to
those used in grinding may be taken, and the tool is then lifted off
and examined. It will be found to be dotted with a few bright points,
produced by the adhesion of glass at the places of contact. These
points are then to be removed in the following manner. An old
three-cornered file is ground on each side till the file marks
disappear, and sharp edges are produced (Fig. 53). This tool is used
as an ink eraser, and it will be found to scrape the paper of the
polishing tool very cleanly and well.

The bright spots are the objects of attention, and they must be erased
by the