In the COMPOUND MICROSCOPE, which has quite superseded the ‘simple microscope’ as an instrument of research, the object is magnified in the first instance by the object-glass, and then remagnified by the eye-piece. It follows, therefore, that the magnifying power of the instrument may be increased either by increasing the power of the object-glass or that of the eye-piece. It must be borne in mind, however, that in increasing the power of the eye-piece we do not magnify the object itself in a greater degree, but simply increase the image of the object formed by the object-glass. Any imperfections which may exist in the latter are thus greatly increased. At first the great drawback to the use of the compound microscope was its deficiency in achromatism; but the researches of Mr Lester and Dr Goring led to the achromatising of the object-glass,
which was the first of the rapid strides towards perfection made by this instrument during the last twenty years. The two most useful object-glasses are the ‘quarter-inch,’ which should magnify from 200 to 220 diameters, and the ‘inch,’ which should magnify from 30 to 40 diameters. The definition of these glasses should be good, and they should transmit plenty of light. Any lines in a structure examined by them should appear sharp and distinct, and there should be no coloured fringes around the object. It is of great importance that the object-glasses are kept perfectly free from dust. A few shreds of wash-leather of the finest quality should be kept in a pill-box for cleaning them. Before rubbing them with the leather they may be breathed upon, but no whiting or liquid of any kind should be used, as each object-glass, being achromatic, is a very delicate piece of workmanship, consisting of two lenses of flint and crown-glass cemented together by Canada balsam. Compound microscopes are now sold by the best London makers at very low prices. A really good instrument, adapted to most of the wants of the chemical, pharmaceutical, or medical student, may be obtained for five guineas.
The following formulæ for the preparation of the chief substances, together with the principal reagents required in the working of the microscope, are from Dr Lionel Beale’s valuable book, ‘How to Work with the Microscope,’[36]
[36] Harrison, 59, Pall Mall.
Reagents—
1. Alcohol, of various strengths.
2. Ether, to dissolve oil globules.
3. Nitric acid (1 part of strong acid to 5 of water)
4. Sulphuric acid (1 to 5).
5. Hydrochloric acid.