There is another microscope constructed on the same principle, which is a very superior instrument, though it does not at first sight present any remarkable difference. It possesses, however, four times the magnifying power of that which has just been mentioned. Instead of two magnifiers, there are four, and several subsidiary articles are sent with it,—such as a condenser, a live box, an aquatic box, and half a dozen slides ready prepared. This instrument costs one sovereign.
But if the reader can by any possibility afford it, let us advise him in the strongest terms to devote three guineas to the purpose, and get a really good instrument. For this small sum a microscope may now be obtained which could not have been purchased for twenty times three guineas only a few years ago. One of these beautiful instruments is seen in the accompanying [illustration]; in which may be seen the tube, with its eye-piece and object-glass, and the stand, containing the stage and the mirror. The arrangement, however, is very different; for the focus is not obtained by sliding the tube up and down, but by turning the large milled heads which we see on a level with the stage, and which raise or depress the tube by means of a rack and pinion. As an extremely high power can be used with this instrument, a still finer adjustment is required, so as to obtain a very accurate focus. This is seen on the front of the tube. The reader will notice that the microscope can be inclined backwards, for it is so made that it can be set to any angle which may best suit the observer. The value of this arrangement is very great, as it permits the observer to sit at his ease in a chair, without being forced to crane his neck over the microscope, and look perpendicularly down. Another advantage attending this arrangement is that the secretions which lubricate the eye do not interrupt the vision, as is apt to be the case when looking directly downwards.
The mirror, too, can be turned in any direction, and its distance from the stage lessened or increased by means of a draw-tube. Three different powers are supplied with this microscope, together with a live-box, dissecting and stage forceps, &c.; and the whole is made so as to admit of additional apparatus. The microscope fits into a neat square box, in which is plenty of room for various articles which will presently be described. These three microscopes can be obtained from Messrs. Baker, 244, High Holborn; and we mention them, not because we wish to make any invidious distinctions between the many excellent opticians who now make microscopes, but because we happen to have used Messrs. Baker’s instruments for some years, and can bear practical testimony to their performance.
Another three-guinea microscope ought, however, to be mentioned. It is the Society of Arts microscope, which is made by Messrs. Field, opticians, of Birmingham. In form it closely resembles the instrument which has just been mentioned, but differs in some of the details, as it possesses a “diaphragm-plate” under the stage for regulating the admission of light, and, instead of three object-glasses and one eye-piece, has two object-glasses and two eye-pieces. Dr. Carpenter mentions that, up to 1861, no less than eighteen hundred of these microscopes had been sold. To this instrument the medal of the Society of Arts was awarded.
Either of these microscopes affords all that an ordinary observer is likely to need; and if he adds a few articles of supplementary apparatus, he will find himself possessed of a microscope that will serve all purposes except scientific controversy.
Presuming that the reader has supplied himself with one or other of the compound microscopes, we will proceed to show the method of using them.
The manipulation of a compound microscope is not so easy as it looks. The possessor of a really good instrument may fail hopelessly in his attempts to see a single object. Now, there are three essential points which a microscopist must attend to,—namely, the correct focus, the proper light, and the preparation of the object. Of these the focus is of course the most important, and can be best obtained as follows:—