When the two last grades are used shorten the strokes to less
than 2 in. When done the glass should be semi-transparent, and is
ready for polishing.
When polishing the speculum, paste a strip of paper 1-1/3 in. wide
around the convex glass or tool, melt 1 lb. of pitch and turn on
to it and press with the wet speculum. Mold the pitch while hot
into squares of 1 in., with 1/4-in. spaces, as in Fig. 1. Then
warm and press again with the speculum, being careful to have all
the squares touch the speculum, or it will not polish evenly. Trim
the paper from the edge with a sharp knife, and paint the squares
separately with jeweler's rouge, wet till soft like paint. Use a
binger to spread it on with. Work the speculum over the tool the
same as when grinding, using straight strokes 2 in. or less.
When the glass is polished enough to reflect some light, it should
be tested with the knife-edge test. In a dark room, set the
speculum against the wall, and a large lamp, L, Fig. 2, twice the
focal length away. Place a large sheet of pasteboard, A, Fig. 2,
with a small needle hole opposite the blaze, by the side of the
lamp, so the light
[Illustration: Detail of Telescope Construction]
from the blaze will shine onto the glass.
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