The microscope: its history, construction, and applications ... / by Jabez Hogg.

  • Jabez Hogg
Date:
1867
Catalogue details

Licence: Public Domain Mark

Credit: The microscope: its history, construction, and applications ... / by Jabez Hogg. Source: Wellcome Collection.

    82/796 (page 56)
    Magnifying Power of Messrs. Powell and LealancCs Achromatic Object-Glasses. Object Glasses. Angular Aperture. Magnifying Power with the -various Eye-Pieces. Price. No. 1. No. 2. No. 3. No. 4. No. 5. Inches. Deg. £ s. 2 14 25 37 50 100 150 2 15 1 28 50 74 100 200 300 3 0 i 70 100 148 200 400 600 5 0 l 95 200 296 400 800 1200 5 5 125 400 692 800 160G 2400 8 8 _k_ 145 000 888 1200 2400 3600 10 10 To 175 800 1184 1600 3200 4800 16 16 Schmidt’s goniometer positive eye-piece, for measuring the angles of crystals, is so arranged as to be easily rotated within a large and accurately graduated circle. In the focus of the eye-piece a single cobweb is drawn across, and to the upper part is attached a vernier. The crystals being placed in the field of the microscope, and care being taken that they lie perfectly fiat, the vernier is brought to zero, and then the whole apparatus turned until the line is parallel with one face of the crystal; the frame-work bearing the cobweb, with the vernier, is now rotated until the cobweb becomes parallel with the next face of the crystal, and the number of degrees which it has traversed may then be accurately read off. To the most complete instruments a set of eye-pieces, consisting of not less than three, is usually made. These differ in power; the longest is always the lowest power, and is marked a. Its angular aperture, which determines the size of the field of view, is generally less than that of the others (if constructed on the Huyghenean plan), being limited by the diameter of the body. It is usually about 20 degrees. The next eye-piece, or middle power, marked B, and the deepest, c, have more than 30 degrees of angular aperture. For viewing thin sections of recent or fossil woods, coal, the fructification of ferns and mosses; fossil-shells, seeds, small insects, or parts of larger ones; molluscs or