The upper part, f g r S, of the opake stage takes out, that the stage for transparent objects may be inserted in its place.
Fig. 4. represents the stage for transparent objects; the two legs 5 and 6, fit into the under part r S of the stage for opake objects; 7 is the part which confines or holds the sliders, and through which they are to be moved; 9 and 10 a brass tube, which contains the lenses for condensing the light, and throwing it upon the object; there is a second tube within that, marked 9 and 10, which may be placed at different distances from the object by the pin 11.
When this stage is used as a single microscope, without any reference to the lucernal, the magnifiers or object lenses are to be screwed into the hole 12, and to be adjusted to a proper focus by the nut 13.
N. B. At the end A B of the wooden body there is a slider, which is represented as partly drawn out at A; when quite taken out, three grooves will be perceived, one of which contains a board that forms the end of the box, the next contains a frame with a greyed glass; the third, or that farthest from the end A B, two large convex lenses.
OF THE LAMP.
Fig. 3, represents one of Argand’s lamps, which is the most suitable for microscopic purposes, on account of the clearness, the intensity, and the steadiness of the light. The following method of managing it, with other observations, is copied from an account given by Mr. Parker, with those he sells.
The principle on which the lamp acts, consists in disposing the wick in thin parts, so that the air may come into contact with all the burning fuel, by which means, together with an increase of the current of air occasioned by rarefaction in the glass tube, the whole of the fuel is converted into flame.
The wicks are circular, and, the more readily to regulate the quantity of light, are fixed on a brass collar with a wire handle, by means of which they are raised or depressed at pleasure.
To fix the wick on, a wood mandril is contrived, which is tapered at one end, and has a groove turned at the other.
The wick has a selvage at one end, which is to be put foremost on the mandril, and moved up to the groove; then putting the groove into the collar of the wick-holder, the wick is easily pushed forward upon it.