The microscope and microscopical technology : a textbook for physicians and students / by Heinrich Frey ; translated from the German and edited by George R. Cutter, from the fourth and last German edition.

Date:
1872
Catalogue details

Licence: Public Domain Mark

Credit: The microscope and microscopical technology : a textbook for physicians and students / by Heinrich Frey ; translated from the German and edited by George R. Cutter, from the fourth and last German edition. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    ment of a nose-piece. This is an apparatus having two or more arms capable of revolving and carrying the ol:)jectives at their peripheral extremities. The mechanism is to be screwed on to the lower end of the microscope tube, the same as a simple objective. The various objectives are brought into position successively by simply turning the arms. Farther movement and accurate centring is controlled by means of a catch. The original nose-piece, invented by Brooke, of London, revolved on a horizontal plane, but by a more recent improvement the objectives which are not in use are elevated obliquely, and only become vertical at the moment they are adjusted to the axis of the microscope tube, so that they do not in any manner interfere with the manipulation of the stage. This accessory is almost indispensable for those who work much with the microscope.] It is a general mistake of beginners, who under-estimate the value of low powers, to use high powers at the very commence- ment of the . examination. As, howe^'er, only the weak ob- jectives afford a somewhat extended field of vision, while with stronger lenses it is extremely small, it results that the employ- ment of weak combinations is of great importance for the si- multaneous survey of the whole, as well as to give the observer the first ideas as to the relation of its several parts. One then gradually passes to the employment of stronger objectives; at first, always with very weak eye-pieces. AVhen working with cylindrical diaphragms it is necessary to vary them, exchanging those with large apertures for those with smaller ones, likewise occasionally exchanging the plane mirror for the concave, and in all cases adjusting as accurately as pos- sible with the micrometer screw. ^Ylieii the observer has found it necessary to make use of his higher powers, he may proceed to employ somewhat stronger eye-pieces ; but he should be sparing in their use. One is soon convinced that less is obtained with them, which results from their optical nature, than would be at first believed. The image is larger, whereby some points may at first appear more distinct. An enlargement is soon arrived at, however, which does not show any more, but rather less, than the weaker of the previously employed eye-pieces, the brightness of the field and the sharp-