Author Description

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. 1865 Excerpt:... up or down by turning the small screw (b). In this instrument the amount of pressure is the force imparted by the screw (b), and it is very considerable; it is equally distributed over the glasses by the ring (c) being swung in the centres (d, d), and by the semicircle (e) having a revolving fitting at (f); the lever (a) can be turned on one side, so as to expose both glasses when they want cleaning, or when the object is to be changed. Wenham's Compressor. Wenham's compressor (figs. 7 & 8) was designed especially for use with the parabolic reflector or achromatic condenser. The bottom plate (a) is very thin, and a circular thin glass is cemented in the middle; the top plate (b) is a thin brass arm, also carrying a circular thin glass cemented to it; the pressure is imparted by a spring or set which is given to the arm (b), and the two pieces of glass will approach or separate according to the direction in which the small milled head (c) is turned; the arm will also turn aside, as in the lever compressor. The simple construction of Wenham's compressor makes it a very easy and convenient instrument to use; it has, however, one or two disadvantages--the two pieces of glass do not move in parallel directions, and the amount of pressure is rather limited. Reversible Compressors. The next two compressors are our own contrivance, and both of them individually combine in one piece of apparatus the excellences of those already described, together with the following new qualities: viz., a parallel and equal compression, with an immediate action up or down; the means of turning the compressor over, so as to see both sides of an object without disturbing it; the use of thin glass only either at top or bottom; and lastly, such restrictions in the thickness of the...