The accessories and appliances of the microscope have become so very numerous, that any attempt to describe them and explain the uses to which they are put would demand more space than I find myself in a position to bestow upon them. I must therefore confine my remarks to those accessories in more general use.
Fig. 154.—The Lieberkühn.
Having described the method of employing transmitted light, I have a few words to add with regard to the illumination of opaque objects by reflected light. A very early and efficient form of opaque illumination is the well-known Lieberkühn. This has not been entirely surpassed by more recent inventions. The concave speculum termed a Lieberkühn, so named after its celebrated inventor, directly reflects down upon the object the light received either from the mirror or bull’s-eye lens. It consists of a silver cap, which slides over the objective ([Fig. 154]), a indicating the lower part of the compound body, and b the objective over which slides the Lieberkühn, c; the rays of light are collected to a focus upon the object at d. The object may either be mounted on a slip of glass, or held by the stage-forceps, f; if very small, or transparent, it may be gummed to the dark well, e, or mounted on a Beck’s opaque disc-revolver.
Fig. 155.—Stage Forceps, for holding objects while under examination.
Fig. 156.—Beck’s Disc-holder.
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the illumination of opaque objects must be more or less one-sided, and therefore, the silver side-reflector has superseded it for general use ([Fig. 157]).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.