Fig. 11, will pass and repass as smoothly as the motion of a telescope, which is controlled in a similar manner.
There is no reason why the optical parts should not be made by the student, but necessary instructions would require a series of articles. Assuming, therefore, that such portions will be purchased, a few words on that head may be necessary.
Fig. 12.
If only one eye-piece is required, select letter B. Next take tube. Fig. 11, to an optician, and ask him to fit a Royal Microscopical Society screw, Fig. 8, in the centre of a wood block. This block and screw must be fastened into one end of the paper tube, and will carry the object-glass.
The last fitting will be the mirror, a reduced drawing of which is shown at Fig. 13.
The mirror should be at least two inches in diameter, and the ring which passes over the rod. Fig. 4, should be split, and about half an inch in breadth, and, being made somewhat too small, will grip the rod, and be free from unsteady movement.
Fig. 13.
To hold the slide upon the stage in position, pass two moderate-sized India-rubber bands upon each side, and a third crosswise near the bottom; a very delicate movement can be given to a slide thus held.
In regard to object-glasses I have little to add. Such as I should have specially recommended are not to be obtained in this country;
