The botanical microscope used by Dr. Withering, is shown in Plate CCCLXXVII. Fig. 14. where A, B, C, are three parallel brass plates. Two wires D and E are rivetted into the upper and lower plates A and C, and the middle plate B is moveable along these wires by two little sockets fixed to it. The two upper plates contain each a magnifying lens of different focal lengths, one of which keeps in their places the sharp point F, the small knife K, and the pliers P.
Before using this microscope, we must unscrew the upper lens, and take out the point, the knife, and the pliers ; and having replaced the lens by screwing it on again, the object is placed on the stage, and moved up or down till it is seen distinctly.
IV. Pocket Botanical and Universal Microscope.
This instrument, which is superior to Dr. Wither ing's, is represented in Plate CCCLXXVIJ. Fig. 15. A small arm AB carries three lenses, two or which at e fixed to the upper par t at B, and the other to the lower part at C; and as these three lenses may be either used separAtely or combined, they afford us seven different magnifying powers. A square pillar AK supports the arm AB. The lower end of this pillar fits into the socket E of the base FG. The stage DL, carrying the pliers NI and a sharp point N, constructed as formerly described, is made to slide up and down the pillar IK. A reflecting mirror H, moving round a horizontal and vertical axis, is fixed into the base FG, and reflects light through the object. In using this microscope, the objects are placed on the stage L ; or, if they are put into ivory sliders, these sliders pass under the stage L. The light is then thrown upon the object by the mirror H, and distinct vision obtained by the motion of the stage. Other ob jects may be fixed in the pliers NI, N, and used as al ready described.
The apparatus accompanying this instrument con sists of three ivory sliders, a pair of nippers, a flat glass, and a concave lens, all of which are fitted to the stage L. By taking out the pin E, the pillar 1K may be turn ed half round, and the base FG used as a handle. The stage DL, instead of being moved by the hand, is fre quently raised and depressed by an adjusting screw.
V. Lyonet's Anatomical Microscope.
The microscope represented in Plate CCCLXXVII. Fig. 16, was employed by M. Lynnet in his microscopical dissection of the caterpillar of the goat moth. It con sists of an anatomical table AB, supported by a pillar ON, screwed into the mahogany box DC. In the table AB, which is prevented from turning round by two steady pins, is an aperture G, exactly over the mirror EF, for reflecting light on the object. A flat or concave glass is placed on the aperture G. for receiving the objects to be dissected. An arm RXZ, composed of several balls and sockets, by which it has an universal motion, is fix ed to the table AB by means of the screw H. The last
arm IZ carries a female screw for receiving a magnify ing lens, as shown at Z. The lens is generally adjust ed to distinct vision of the object by the hand, though a small motion may be given to it by the screw at H. Another chain of balls and sockets is sometimes used for holding an illuminating lens. The mirror EF can also be taken from its place at K, and fixed by a clamp to any part of the table AB.
In using the dissecting table, the instrument should stand upon a firm table, the left side of the observer being near a light window, and the side DL towards his breast. The observations should be made with the left eye ; and in dissecting, the two elbows should be supported on the table which holds the microscope, the hands resting against the board AB, to give it greater steadiness. See Lyonet's Traite Anatomiyue de to Che nille, E.7c.
VI. Wilson's Pocket Microscope.
The microscope invented by Nit.. Wilson has been long in use. The body of it is represented by AB, (Plate CCCLXXVII. Fig. 17.) and is made either of brass, silver, or ivory. Another tube, with a long fine threaded small screw upon its circumference, screws unto the body AB. A convex lens D is screwed into the end of the tube CC, and its area may be increased or diminished by placing upon it one or other of the two concave apertures of thin brass, which are necessary when the highest magnifiers are employed. Two thin plates of brass are shown at E, within the body of the microscope ; and one of them is bent into an arched or semicylindrical cavity, shown in the figure, for the pur pose of receiving a tuhc of glass. At the eye-end G of the microscope is a female screw for receiving the different magnifiers. A spiral steel spring II, abutting with one extremity against the end G and with the other against the plate of brass E, serves to keep the plates in a proper position, and to act against the long screw C. The microscope is held by the ivory handle I. Seven different magnifying glasses, six of which are set in cells, as shown at K, are numbered from I to 6, the least numbers being the highest magnifiers. The seventh, or least magnifier, is set in a small tube, in order that it may be held in the hand for viewing any large object. The objects are held in an ivory slider M. Six sliders like this of ivory, and one of brass, generally accompany ing the instrument. A brass slider, not represented in the figure, is sometimes added, for the purpose of con fining any small object, in order that it may be examined without being crushed. A pair of forceps and a hair brush are used, as shown at H and Q, Fig. 13. A glass tube, for holding living objects, such as frogs, fishes, &c. is shown at P.