Leitz of Jena, supplies two good and cheap microscopes for £3 10s. and £5. They are not, however, of uniform excellence, and they should be carefully tested by some competent judge before the purchase is completed. Leitz immersion lenses are cheap, and often extremely good, but should be carefully tested beforehand, as their quality is not quite uniform. The microscopes can be obtained from Mr. A. Frazer, Teviot Place, Edinburgh.
The “Bacteriological” microscope, made by Messrs. Swift, of Tottenham Court Road, is one with which no one can be disappointed. It is sold with Abbe’s condenser, triple nose-piece, 1/6 in., and a 1/12 in. immersion objective, for just under £20. Both stand and lenses are turned out in Swift’s first-class style, and those who can afford the initial outlay will not regret it. Or the stand may be purchased, and the objectives and accessories added singly from time to time.
Among Continental makers, excellent microscopes for histological work are turned out by many makers. Zeiss’s lenses stand deservedly high in reputation, as no faulty Zeiss lens ever leaves the works, and their optical properties are nearly perfect. For this guarantee, however, the purchaser has to pay somewhat higher prices, but the money is well invested. Zeiss’s agency is at 29 Margaret Street, Regent Street, W.
Reichert, of Vienna, sells microscopes and lenses which are modelled on the lines of those of Zeiss, and though cheaper are often equal to them in excellence, but the quality is not quite uniform. His instruments can be obtained through any optician, but his agent in this country is Mr. A. Frazer, Teviot Place, Edinburgh.
Before buying a microscope the student should obtain an illustrated price list from any of the firms mentioned above, and, having selected an instrument, he should test it very carefully, or better get some experienced friend to test it for him, before deciding to purchase it. Delicate test objects such as diatoms, scales of butterfly’s wing, or a stained specimen of micro-organisms should be employed. The coarse and fine adjustments should be tried. They should work freely and smoothly and without any delay. The definition of the lens must be tested with the fine objects mentioned. The field should be quite flat, i.e., every part should be in focus at the same time, and the definition should be perfectly sharp and accurate, and the test objects without double contour. The field should be totally free from prismatic colours. If there is a halo of colour around the objects it indicates a defect in the optical properties of the objective, and another should be selected.
A microscope must always be treated with the greatest care. Jars and falls tend to slightly loosen and shift the lenses, and to permanently impair its optical properties. Dust must be most carefully excluded. This is best effected by keeping the instrument under a glass bell jar when not in use. The lenses should be wiped as little as possible, and when it is necessary, very soft chamois leather should be employed. The microscope must be kept in a dry room, or the brass work will soon tarnish and the steel parts will tend to rust.