Practical Microscopy: Manipulation, and Mode of Using the Microscope. In this chapter it will be my aim to discuss the best practical methods of employing the microscope and its appliances to the greatest advantage. First, the student should select a quiet room for working in, with, if possible, a northern aspect, free from all tremor occasioned by passing vehicles. The table selected for use should be firm, and provided with drawers, in which his several appliances can be kept ready to hand. The microscope must be placed at such an inclination as will enable him to work in comfort, and without putting strain on the muscles of the neck or fatiguing the eyes. The next important point is that of light. Daylight, in some respects, is an advantage; this should come from a white cloud on a bright day, but as a rule more satisfactory results will be obtained by using a well-made lamp, as this can be controlled with ease, and used at a proper height and distance from the microscope. To have a good form of lamp is as much to be desired for the student as for those engaged in the more advanced work of microscopy. Whatever the source of light we must on no account over-illuminate. The object having been placed on the stage of the microscope, the body should be racked down to within a quarter or half an inch of the specimen, and then, while looking through the eye-piece, should be slowly withdrawn until a sharp image comes into view. The fine adjustment may now be used for the more delicate focussing of the several parts of the field. Accurate adjustment of focus is required when using a 1/4-inch objective; details of the object, as striæ, being brought into view when a stronger light is thrown obliquely upon them from the mirror. If a 1-inch objective is used the light often proves to be in excess of what is required, and this must be regulated by the aid of the diaphragm. The iris diaphragm, made to drop into the under-stage, is more generally employed, as when racked up to the object it affords every necessary graduation of illumination. [Illustration: Fig. 201.--Bull’s-eye Lens.] To illuminate opaque objects the light should be thrown upon them from above by the bull’s-eye lens (Fig. 201). The focus of such a lens and the lamp placed at four inches from it, is about three inches for daylight, or two inches for artificial light. A large object may be placed upon the stage of the microscope at once, but smaller objects are either laid on a glass slide or held in the stage forceps. When illuminating objects from above all light from the mirror, or that which might enter the objective from below the stage, should be carefully excluded. _Dark-field illumination_ is a means of seeing a transparent object as an opaque one. The principle, however, is that all the light shall be thrown from below the object, but so obliquely that it cannot enter the object-glass unless interrupted by the object; this is best accomplished by _Wenham’s Parabola_.