. A practical treatise on the use of the microscope, including the different methods of preparing and examining animal, vegetable, and mineral structures. Microscopes; Microscopy. 140 PRACTICAL TREATISE ON THE MICROSCOPE. much stouter, and fits accurately upon the raised object- plate. Troughs for Chara and Polyps.—These consist of two plates of glass cemented together, with strips of the same material, or of metal between them, to form the sides of the trough; one of these, as described by Mr. Varley, in the forty-eighth vol. of the Transactions of the Society of Arts, is represented by fig.
. A practical treatise on the use of the microscope, including the different methods of preparing and examining animal, vegetable, and mineral structures. Microscopes; Microscopy. 140 PRACTICAL TREATISE ON THE MICROSCOPE. much stouter, and fits accurately upon the raised object- plate. Troughs for Chara and Polyps.—These consist of two plates of glass cemented together, with strips of the same material, or of metal between them, to form the sides of the trough; one of these, as described by Mr. Varley, in the forty-eighth vol. of the Transactions of the Society of Arts, is represented by fig. 93. c is a bottom-plate of stout glass, upon which is cemented with pitch and bees'-wax a thin cover, d, with slips of glass between it and the bottom-plate, to form the sides. The cover, d, is not so broad as the plate, c, in order Fig. 93. that a slip of chara may be more readily placed in the trotigh, as it can be first laid upon c, and then gradually slid down between it and the cover, d. In order to render the trough more manageable, it may be cemented to a larger bottom-plate, a b, by Canada balsam; but it will be found far more advantageous if the bottom-plate itself be as large and as broad as a h, and if the cover, d, be cemented to it and not to another plate, as then two extra surfaces will be dispensed with. Mr. Varley informs us that a piece of wire bent into the shape of the slips of glass represented in the figure, and covered thickly with a cement composed of bees'-wax and pitch, will form an excellent substitute for the slips, and look very neat; the cements of Canada balsam or sealing wax are much too brittle to last long, as a sudden jar will cause them to give way. Messrs. Smith and Beck supply with their microscopes a larger and much thicker trough for chara and polyps, as represented by fig. 94; the front is composed of much thinner glass than the back, and the method adopted of confining objects near to the front varies according to circum- stances. One
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