BOTANICAL MAGNIFIERS.
Since botany has been cultivated with so much ardor, it has been found necessary to contrive some very portable instrument, by which the botanist might investigate the object of his pursuits as it rises before him. [Plate VIII.] Fig. 7 and 8, represent two of the most convenient sort.
In the tortoiseshell case, Fig. 7, three lenses are contained, d, e, f, of different foci, which are all made to turn into the case, and may be used combined or separately. The three lenses in themselves afford three different magnifying powers; by combining two and two, we make three more; and the three together make, a seventh magnifying power. When the three lenses are used together, it is best to turn them into the case, and look through the hole, for more distinctness, and the exclusion of superfluous light. In the case, Fig. 8, are also three lenses, g, h, i, of different magnifying powers, that all turn up, and shut into the case; but these are not capable of combination.
DESCRIPTION OF A PORTABLE MICROSCOPE AND TELESCOPE. [Plate VIII.] Fig. 1, to 6.
The telescope is one of those which are composed of several sliding drawers or tubes, for the convenience of being put into the pocket; the sliding tubes are made of thin brass, the outside tube of mahogany. The sliding tubes are contrived to stop, when drawn out to a proper length, so that by applying one hand to the outside tube, and the other hand to the end of the smallest tube, the telescope may at one pull be drawn out to its full length; then any of the tubes (that next the eye is most generally used) may be pushed in gradually, while you are looking through it, till the object is rendered distinct to the eye. To make the tubes slide properly, they all pass through short springs or tubes; these springs may be unscrewed from the ends of the sliding tubes, by means of the milled edges which project above the tubes, and the tubes taken from each other if required, and the springs set closer if at any time they be too weak.
Fig. 5 represents the exterior tube of the telescope, which is to be unscrewed from the rest, at m l, as it does not make any part of the microscope; the cover, k, which protects the object-glass, serves also as a box to contain two ivory wheels, Fig. 1 and 2, with the objects, and a small mirror, Fig. 6.
Fig. 4 is a view of this cover when taken off: unscrew the top part of it, and the mirror, Fig. 6, may be taken out; unscrew the cover of the lower part, and you will find therein the two circular object-wheels above mentioned.
Fig. 3 represents the three internal tubes of the telescope, which constitute the microscopic part thereof. Draw the tubes out in the manner as shewn in the figure; then at the inside, but at the lower end of the exterior tube, a, you will find a short tube, which serves as a stage to hold the object and support the mirror; pull this tube partly out, and turn it, so that a circular hole which is pierced in it may coincide with a similar hole in the exterior tube. This tube is represented as drawn out at Fig. 3, the mirror, Fig. 6, placed therein at b c, and the transparent object-wheel fixed at a.
Fig. 1 represents the slider with transparent objects.
Fig. 2, that with the opake. They are made of ivory, and turn on a pin at the center; the slit end of this pin fits on the edge of the tube, which is then to be pushed up, so that the lower end of the exterior tube may bear lightly on the upper side of the slider, agreeable to the view which is given at a, Fig. 3. Now push down the second tube till the milled part falls on the milled edge of the extreme tube, being careful of the circular hole in the exterior one. Nothing now remains to be done but to adjust for the focus, which is effected by pushing in the tube R, and moving only the first, n.
The instrument may be used in two ways for transparent objects: first, in a vertical position, when the light is to be thrown on the object by the mirror, b c; or it may be examined by looking up directly at the light; in the latter case the mirror must be taken away. In viewing opake objects the mirror is not used; as much light as possible must be admitted on them through the circular holes of the tubes. Any object may be viewed by first pushing in the tube, R, and then bringing the tube, n, to its focal distance from the object. The telescope, when shut up, is about eight inches in length, and when drawn out, is about twenty inches. It is of the achromatic construction.
DESCRIPTION OF AN INSTRUMENT FOR CUTTING THIN TRANSVERSE SECTIONS OF WOOD, [Plate IX.] Fig. 1.
It consists of a wooden base, which supports four brass pillars; on the top of the pillars is placed a flat piece of brass, near the middle of which there is a triangular hole. A sharp knife which moves in a diagonal direction, is fixed on the upper side of the afore-mentioned plate, and in such a manner, that the edge always coincides with the surface thereof. The knife is moved backwards and forwards by means of the handle, a. The piece of wood is placed in the triangular trough, which is under the brass plate, and is to be kept steady therein by a milled screw which is fitted to the trough; the wood is to be pressed forward for cutting, by the micrometer screw, b. The pieces of wood should be applied to this instrument immediately on being taken out of the ground, or else they should be soaked for some time in water, to soften them, so that they may not hurt the edge of the knife. When the edge of the knife is brought in contact with the piece of wood, a small quantity of spirit of wine should be poured on the surface of the wood, to prevent its curling up; it will also make it adhere to the knife, from which it may be removed by pressing a piece of blotting paper on it.
Fig. 2, is an appendage to the cutting engine, which may be used instead of the micrometer screw, being by some practitioners preferred to it. It is placed over the triangular hole, and kept flat down upon the surface of the brass plate, while the piece of wood is pressed against a circular piece of brass which is on the under side of it. This circular piece of brass is fixed to a screw, by which its distance from the flat plate on which the knife moves may be regulated.[38]
[38] Many other kinds of cutting engines have been constructed, but the specimens from them have not yet appeared with that perfection which is requisite to this sort of objects; whether it lies in the preparation of the woods, or engine, I do not take upon me to determine. Mr. Custance has certainly produced the most exquisite. Edit.
CHAP. IV.
GENERAL INSTRUCTIONS FOR USING THE MICROSCOPE AND PREPARING THE OBJECTS.
As the advantages which are obtained from any instrument are considerably increased, if it be used by a person who is master of its properties, attentive to its adjustments, and habituated by practice to the minutiæ of management, it is the design of this chapter to point out those circumstances which more peculiarly require the attention of the observer, and to give such plain directions, as may enable him to examine any object with ease; to shew how he may place it in the best point of view, and if necessary, prepare it for observation.
A small degree of diligence will render the observer master of every necessary rule, and a little practice will make them familiar and habitual: the pains he takes to acquire these habits will be rewarded by an increasing attachment to his instrument, and the wonders it displays. Let him only persevere till he has overcome the natural indolence that opposes the advancement of every kind of knowledge, and he will most assuredly find himself very amply recompensed, by the gratification arising from the acquisition of a science that has the unlimited treasures of INFINITE WISDOM for the object of its researches: and his mind being strengthened by the victory it has gained, will be more keen in perceiving, and more patient in the investigation of truth.
It has long been a complaint,[39] that many of those who purchase microscopes are so little acquainted with their general and extensive usefulness, and so much at a loss for objects to examine by them, that after diverting themselves and their friends some few times with what they find in the sliders, which generally accompany the instrument, or perhaps two or three common objects, the microscope is laid aside as of little further value: whereas no instrument has yet appeared in the world capable of affording so constant, various, and satisfactory an entertainment to the mind. This complaint will, I hope, be obviated by these Essays, in which I have endeavoured to make the use of the microscope easy, point out an immense variety of objects, and direct the observer how to prepare them for examination.
[39] Baker’s Microscope made Easy, p. 51.
The subject treated of in this chapter naturally divides itself into three heads: the first describes the necessary preparation and adjustment of the microscope; the second treats of the proper quantity of the light, and the best method of adapting it to the objects under examination; and the third shews how to prepare and preserve the various objects, that their nature, organization, and texture, may be properly understood.