. On microscopical manipulation : being the subject matter of a course of lectures delivered before the Quekett Microscopical Club, January-April, 1869. n a convenientsetting, so that it may be fitted over the eye-piece inthe place of the cap, which is of course removed. Alens is sometimes attached to the lower part of thecamera lucida, between the eye and the paper ; thisis of use to persons who cannot see the drawingdistinctly at the usual distance, about ten inches,and may be either convex or concave, according tothe special requirement of those using it. A small steel disc, known as Soemme
. On microscopical manipulation : being the subject matter of a course of lectures delivered before the Quekett Microscopical Club, January-April, 1869. n a convenientsetting, so that it may be fitted over the eye-piece inthe place of the cap, which is of course removed. Alens is sometimes attached to the lower part of thecamera lucida, between the eye and the paper ; thisis of use to persons who cannot see the drawingdistinctly at the usual distance, about ten inches,and may be either convex or concave, according tothe special requirement of those using it. A small steel disc, known as Soemmerings mirror,placed at an angle of 45°, is used by somemicroscopists. The polished disc is smaller thanthe pupil of the eye ; so that, while the image fromthe microscope is viewed by the centre of the pupil,its circumference is employed in viewing the pencil-point and paper, upon which the image appears tobe projedled, as in the camera lucida. Another contrivance, and one which has the * Ante, p. no,L 2 148 MICROSCOPICAL MANIPULATION. recommendation of being procured at a -very smallcost, is the neutral tint reflector (Fig. 40). It con- FiG. sists of a small plate of glass, with surfaces accu-rately parallel, and slightly coloured, so as to improveits reflecting qualities, but not sufficiently dark toprevent the paper from being easily seen through is placed, as before, at an angle of 45°. As theinstrument is commonl}^ constructed, the tinted glassis a fixture, and the setting too long; so that themirror is removed to a greater distance than is advan-tageous from the front glass of the eye-piece ; thiscontracts the field so much, when any but an eye-piece of low power is employed, that it is almostuseless. This defeCt is remedied in the form hererepresented, in which the mirror is brought as closeas possible to the eye-glass. The tinted glasses arealso removable, so that a change of tint may be made,as it will be found sometimes that one tint suits theeye better
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