This holder will be found useful for the examination of opaque or other objects that cannot be conveniently held by the stage forceps, the specimen being temporarily attached to it by gum or gold size. The holder is intended to rotate, so that every portion of the object can be brought into view. In this way it will be found useful in the study of insects, foraminifera, &c. With the Lieberkühn, however, the illumination of opaque objects must be more or less one-sided, and therefore, the silver side-reflector has superseded it for general use (Fig. 157). To ensure a more perfect illumination of the object, the bull’s-eye lens should also be used. Mr. Sorby devised a reflector to fit over the objective. It consists of a semi-circular cap; is, in short, a modification of the parabolic reflector. The light from the mirror can, by slightly varying its inclination, be brought into use with this reflector. The silver side-reflector is usually made with a ball-and-socket joint, so that it can be turned in any direction. It is secured to the stage of the microscope by the pin, which drops into a hole purposely drilled to receive it, and facility given for turning up and down, or in any position. If daylight is used the microscope should be placed in such a position that the light from a white cloud falls upon the speculum, but the light of the lamp is far more manageable for use with the reflector. [Illustration: Fig. 157.--Silver Side-reflector.] The Lieberkühn is only intended to be used with low powers--a 2-inch, 1/2-inch and a 2/3-inch. Such objects as the elytra of the diamond and other beetles are well suited for examination. [Illustration: Fig. 158.--Sorby’s Modification of the Parabolic Reflector.] While experimenting with a parabolic reflector (Fig. 158), Mr. Sorby saw the value of examining objects under every kind of illumination. As on viewing specimens of iron and steel with this reflector he found that, from the great obliquity of the illumination obtained, the more brilliantly polished parts of the specimen reflected the light beyond the aperture of the objective, and these could not be distinguished from those parts which absorbed light, he thereupon proceeded to place a small flat mirror in front of the objective, and cover half its aperture, and at the same time stop off by means of a semi-cylindrical tube the light from the parabolic reflector. This arrangement produced the reverse appearance of that first employed, and it proved to be a useful aid in determining structure. The Bull’s-eye Condensing Lens.