Have ready six large dishes, then take 2 lb. flour emery and mix in 12 qt. of water; immediately turn the water into a clean dish and let settle 30 seconds; then turn it into another dish and let settle 2 minutes, then 8 minutes, 30 minutes and 90 minutes, being careful not to turn off the coarser emery which has settled.  When dry, turn the emery from the 5 jars into 5 separate bottles, and label.  Then take a little of the coarsest powder, wetting it to the consistency of cream, and spread on the glass, work as before (using short straight strokes 1-1/2 or 2 in.) until the holes in the glass left by the grain emery are ground out; next use the finer grades until the pits left by each coarser grade are ground out.  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.  Place the speculum S, Fig. 2, so the rays from the needle hole will be thrown to the left side of the lamp (facing the speculum), with the knife mounted in a block of wood and edgeways to the lamp, as in K, Fig. 2.  The knife should not be more than 6 in. from the lamp.  Now move the knife across the rays from left to right, and look at the speculum with the eye on the right side of the blade.  When the focus is found, if the speculum is ground and polished evenly it will darken evenly over the surface as the knife shuts off the light from the needle hole.  If not, the speculum will show some dark rings, or hills.  If the glass seems to have a deep hollow in the center, shorter strokes should be used in polishing; if a hill in the center, longer strokes.  The polishing and testing done, the speculum is ready to be silvered.  Two glass or earthenware dishes, large enough to hold the speculum and 2 in. deep, must be procured.  With pitch, cement a strip of board 8 in. long to the back of the speculum, and lay the speculum face down in one of the dishes; fill the dish with distilled water, and clean the face of the speculum with nitric acid, until the water will stick to it in an unbroken film.