1. To throw the light upon the object. The flame of the lamp is to be placed rather below the center of the glass semiglobe n, and as near it as possible; the concave mirror o must be so inclined and turned, as to receive the light from the semiglobe; and reflect it thence upon the object; the best situation of the concave mirror, and the flame of the lamp, depends on a combination of circumstances, which a little practice will best point out.
2. To regulate the guide for the eye, or to place the center of the eye piece L, so that it may coincide with the focal point of the lenses, and the axis of vision. Lengthen and shorten the tubes M N by drawing out or pushing in the inner tube, and raising or depressing the eye-piece M L, till you find the large lens, which is placed at the end A B of the wooden body, filled by an uniform field of light, without any prismatic colours round the edge; for, till this piece be properly fixed, the circle of light will be very small, and only occupy a part of the lens; the eye must be kept at the center of the eye-piece L, during the whole of the operation; which may be rendered somewhat easier to the observer, on the first use of the instrument, if he hold a piece of white paper parallel to the large lenses, removing it from or bringing it nearer to them, till he finds the place where a lucid circle, which he will perceive on the paper, is brightest and most distinct, then to fix the center of the eye-piece to coincide with that spot; after which a very small adjustment will set it perfectly right.
3. To adjust the lenses to their focal distance. This is effected by turning the pinion a, the eye being at the same time at the eye-piece L. I often place the grey glass before the large lenses, while I am regulating the guide for the eye, and adjusting for the focal distance.
If the observer, in the process of his examination of an object, advance rapidly from a shallow to a deep magnifier, he will save himself some labour by pulling out the internal tube at O.
The upper part f g r s of the stage, is to be raised or lowered occasionally, in order to make the center of the object coincide with the center of the lens at O.
To delineate objects, the grey or rough ground glass must be placed before the large lenses; the picture of the object will be formed on this glass, and the outline may be accurately taken, by going over the picture with a pencil.
The opake part may be used in the day-time without a lamp, provided the large lenses at A B be screened from the light.
TO USE THE LUCERNAL MICROSCOPE IN THE EXAMINATION OF TRANSPARENT OBJECTS.
The microscope is to remain as before: the upper part f g r s of the opake stage must be removed, and the stage for transparent objects, represented at Fig. 4, put in its place; the end, Fig. 9 and 10, to be next the lamp.
Place the rough glass in its groove at the end A B, and the objects in the slider-holder at the front of the stage; then transmit as strong a light as you are able on the object, which you will easily do, by raising or lowering the lamp.