The microscope and its revelations . yuseful to introduce into the eye-piece, just over the diaphragm,a small steel hand pointiiig to nearly the centre of the field; I 2 116 ACCESSORl APPARATUS. to whose extremity the particular portion of the image whichthe observer is intended to look-at, is to be brought by movingthe object. The hand may be so attached, as to be readilytumed-back when not required; leaviug the field of the eye-piece quite free. This little contrivance, which was devisedby Mr. J. Quekett, is appropriately termed by him the Camera Lucida.—Various contrivances ma
The microscope and its revelations . yuseful to introduce into the eye-piece, just over the diaphragm,a small steel hand pointiiig to nearly the centre of the field; I 2 116 ACCESSORl APPARATUS. to whose extremity the particular portion of the image whichthe observer is intended to look-at, is to be brought by movingthe object. The hand may be so attached, as to be readilytumed-back when not required; leaviug the field of the eye-piece quite free. This little contrivance, which was devisedby Mr. J. Quekett, is appropriately termed by him the Camera Lucida.—Various contrivances may be adaptedto the eye-piece, in order to enable the observer to see theimage projected upon a surface whereon he may trace its out-lines. The one most generally employed is the CameraLucida prism contrived by Dr. Wollaston for the general pur-poses of delineation; this being fitted on the front of the eye-piece, in place of the cap by which it is usually Microscope being placed in a horizontal position, as Fig. Microscope arranged with Camera Lucida for Dra\vlng or Micrometry. shown in Eig. 34, the rays which pass through the eye-piece into the prism, sustain such a total reflection from itsoblique surface, that they come to its upper horizontal surfaceat right angles to their previous diicction; and the eye beingso placed over the edge of this suiface, that it receives theserays from the prism through part of the pupil, whUst it looks CAMEEA LUCID A. 117 beyond the prism, dowu to a wMte-paper surface on the table,with the other half, it sees the image so strongly and clearlyprojected upon that surface, that the only difficulty in tracingit arises from a certain incapacity which seems to exist insome iadividuals, for seeing the image and the tracing-point atthe same time. This difficulty (which is common to aU. in-struments devised for this purpose) is lessened by the inter-position of a slightly-convex lens in the position shown in thefigure, between the
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Keywords: ., bookcentury1800, booksubjectmicroscopes, booksubjectmicroscopy
