MICROSCOPE (Fr., Microscope ; Ger., Mi kroskop) The simple microscope, which was the earliest type of instrument, consists of a stand provided with a single lens or combination of lenses known as the objective, which is focused by mechanical means. This type of microscope is still used in laboratories for dissecting work. The compound microscope is fitted with an arrangement by which the image given by the objective is still further magnified by another lens or combination of lenses known as the eyepiece or ocular. A compound microscope is usually provided with a coarse and fine adjust ment for focusing, the former being used for low magnifications and the latter for high magnifications. The illustration shows a typical instrument. The foot or base is usually of either horseshoe or tripod form. The " limb " carries the focusing apparatus and the body tube with objectives and eyepiece. The draw tube, a smaller tube, sliding or moving by rack and pinion, inside the body-tube, receives the eyepiece or ocular, and enables the separation of objective and eyepiece to be varied at will. The draw-tube is also useful for objectives of very low power which require a longer working distance than the coarse adjustment will allow, the lower end of the tube being provided with a thread to receive the objective. The stage,
which supports the object, is provided with clips to secure the glass slides, and is sometimes fitted with mechanical movements to enable the object under the lens to be accurately adjusted. The sub-stage condenser, for use with high powers, is fixed beneath the stage and focuses the light upon the object which is being examined. In the stage is an aperture in order that transparent specimens may be illuminated by light reflected from the mirror beneath the stage. To facilitate the operation of changing the objective for one of another power, a swivel lens holder, known as a nosepiece, and allowing of the use of several objectives of various powers, can be screwed into the lower end of the micro scope tube, and high or low power objectives can be brought into use by merely turning the nosepiece on the pivot. Most microscopes are inclinable ; that is, the instrument can be brought over to a horizontal position for photo micrography.