Microscopic Cabinet of Select Animated Objects; With a Description of the Jewel and Doublet Microscope, Test Objects, &C

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1832 Excerpt: ...in changing them, and the difficulty of finding the thread, render this plan objectionable. Hence many observers have had the threads turned off the magnifiers, and have allowed them to drop in. The disadvantage now is, that the instrument cannot be used in any but a vertical position, or they fall out. These difficulties are obviated in my plan, by fitting the one to the other, and cutting open the ring (b), to make the magnifiers spring into it. Simple as this contrivance is, it will be found of no small importance to the practical microscopist. On the under side of the arm is a triangular block, which fits into the triangular tube; it is split down the front, to spring tight. The black disc or shade, figure 4, prevents all superfluous light from entering the eye. In high powers, when the quantity of light admitted by the lens is small, this contrivance is very useful, as, without it, the excitement of the eye by extraneous light, destroys the sharpness and delicacy of the object. Figure 6 exhibits the microscope in a vertical position, for dissecting, and other purposes, when the object under examination must be in an horizontal plane. This, however, is the worst position for observation, and should always be avoided, if possible, as it is injurious to the eye. In this case the stage is used. When the observer is desirous of employing this instrument for regular dissections, it is advisable to remove it altogether from the stand, and clamp it firmly to a table or board, and thus the maximum of stability may be obtained. The stage may also be enlarged, to admit the fingers, or the hands may be supported on blocks of wood of a suitable height, resting on the table. I ought not to omit to state, that it is essential, in a complete dissecting microscope, to ...