Читать книгу Essays on the Microscope - George Comp Adams - Страница 31

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The chief imperfections of Cuff’s microscope, as well as of others formerly made, are, their construction rendering them only compound microscopes, the body of the instrument having but a fixed position over the object, and the smallness of the field of view by the old construction of the glasses in the body. To obviate these defects, as well as for the application of material improvements, the late Messrs. Martin and Adams, and the present Messrs. W. and S. Jones, have constructed this kind of microscope in various ways. Two microscopes by the latter artists, which I am now going to describe, appear to me to be the best of any hitherto invented.

Fig. 1 is a representation of the second best sort of compound microscopes. The improvements, though few in number, are essential to the use thereof. The field of view is considerably larger than in the former microscope. The stage and the mirrors are both moveable, so that their respective distances may be easily varied. The magnifiers may be moved about over the object. There is also a condensing glass, for increasing the density of the light, when it is reflected by the mirror from a candle or lamp. It is furnished with two mirrors, one plane and the other concave, and may likewise be used as a complete single microscope.

A B, Fig. 1. represents the body of the microscope, containing a double eye glass, and a body glass; it is here shewn as screwed to the arm C D, from whence it may be occasionally removed, either for the convenience of packing, or when the instrument is to be used as a single microscope.

The eye glasses and the body glasses are contained in a tube which fits into the exterior tube A B; by pulling out a little this tube, when the microscope is in use, the magnifying power of each lens is increased.

The body A B of the microscope is supported by the arm C D; this arm is moveable in a square socket cut in the head that is connected to the main pillar E F, which is screwed firmly to the mahogany pedestal G H; there is a drawer to this pedestal, which holds the apparatus. This arm may be slid backwards and forwards in its socket, carrying the magnifiers and the body of glasses, and also turned horizontally quite round upon the pillar, giving a general motion all over the object on the stage below; which is a material improvement and advantage of this microscope over a similar one described in the former edition of this work, as any unavoidable motion of the living object to be viewed may be followed, by the observer’s hand moving the arm C D as the object changes its place.

N I S is the plate or stage which carries the slider-holder K, this stage is moved up or down the pillar E F, by turning the milled nut M; this nut is fixed to a pinion, that works in a toothed rack cut on one side of the pillar. By means of this pinion the stage may be gradually raised or depressed, and the object adjusted to the focus of the different lenses.

K is the slider-holder, which fits into a hole that is in the middle of the stage N I S; it is used to confine and guide either the motion of the sliders which contain the objects, or the glass tubes that are designed to confine small fishes, for viewing the circulation of the blood. The sliders and tubes are to be passed between the two upper plates.

L is a brass tube, in the upper part of which is fixed the condensing lens before spoken of; it screws into the wire arm a, which is placed in the hole I of the stage, with the glass underneath, and may be set at different distances from the object, according to its distance from the mirror or the candle.

O is the frame which holds the two reflecting mirrors, one of which is plane, the other concave. These mirrors may be moved in various directions, in order to reflect the light properly, by means of the pivots on which they move, in the semicircle Q, and the motion of the semicircle itself on the pin R; the concave mirror generally answers best in the day-time; the plane mirror combines better with the condensing lens in L, and a lamp or candle at night.

At S is a hole and slit for receiving either the nippers b, or the fish-pan c; when these are used, the slider-holder K must be removed.

T, a hole to receive the pin of the convex lens and illuminator d.

There are six magnifying lenses contained in a brass wheel screwed in a circular brass box P; this wheel is moveable about its center with the finger, and stops by a click when the magnifiers are each centrally under the body A B above, or the hole in the arm C D. They are marked from No. 1, to 6, and the proper number shewn in a small opening made in the side of the brass box. This wheel P screws into the arm C D, and may occasionally be taken off to admit of the silver speculum, or a single magnifier, hereafter to be described.

There is a small line cut on the edge of the arm C D, which must be brought to the right hand edge of its socket, in order to center the magnifier to the body and the stage.

By unscrewing the body A B, the single magnifiers in the wheel P being then only left, the instrument readily forms a single microscope.

A small pocket hand single or opake microscope may easily be extracted from this apparatus. When the body A B is screwed off, and the arm C D slipt away from its frame with the wheel of magnifiers, and the forceps, wire, and joint b applied to it, by a hole made in the arm for that purpose, as represented at V, it is then ready for the examination of any small object that may present itself in the garden, &c. and will be found very convenient whenever the whole instrument is not required.