cheaper.]

[Illustration with caption: A VERY PRIMITIVE MOUNTING FOR A
TELESCOPE.]

The tube for the telescope may be made of paper, by pasting a
great number of thicknesses around a long wooden cylinder. A yet
better tube is made of a simple wooden box. The best material,
however, is metal, because wood and pasteboard are liable both to
get out of shape, and to swell under the influence of moisture.
Tin, if it be of sufficient thickness, would be a very good
material. The brighter it is kept, the better. The work of fitting
the objective into one end of a tin tube of double thickness, and
properly adjusting it, will probably be quite within the powers of
the ordinary amateur. The fitting of the eye-piece into the other
end of the tube will require some skill and care both on his own
part and that of his tinsmith.

Although the construction of the eye-piece is much easier than
that of the objective, since the same accuracy in adjusting the
curves is not necessary, yet the price is lower in a yet greater
degree, so that the amateur will find it better to buy than to
make his eye-piece, unless he is anxious to test his mechanical
powers. For a telescope which has no micrometer, the Huyghenian or
negative eye-piece, as it is commonly called, is the best. As made
by Huyghens, it consists of two plano-convex lenses, with their
plane sides next the eye, as shown in the figure.

[Illustration with caption: THE HUYGHENIAN EYE-PIECE.]