. The microscope; an introduction to microscopic methods and to histology. Microscopes. CH. /'] DRAWING WITH THE MICROSCOPE 125 upper one. A small oval hole is then cut out of the center of the sil- vered surface and the two prisms are cemented together in the form of the original cube with a perforated 45 degree mirror within it (Fig. 109, a b). The upper surface of the cube is covered by a perforated metal plate. This cube is placed over the ocular in such a way that the light from the microscope passes through the hole in the silvered face and thence directly to the eye. Light from the draw
. The microscope; an introduction to microscopic methods and to histology. Microscopes. CH. /'] DRAWING WITH THE MICROSCOPE 125 upper one. A small oval hole is then cut out of the center of the sil- vered surface and the two prisms are cemented together in the form of the original cube with a perforated 45 degree mirror within it (Fig. 109, a b). The upper surface of the cube is covered by a perforated metal plate. This cube is placed over the ocular in such a way that the light from the microscope passes through the hole in the silvered face and thence directly to the eye. Light from the drawing surface is reflected by a mirror to the silvered surface of the prism and reflect- ed by this surface to the eye in company with the rays from the microscope, so that the two fields appear as one, and the image is seen as if on the drawing surface (Figs. 109, 114). It is designed for use with a vertical micro- scope, but see § 1S4. Fig. 112. Wollaston's Camera Lucida, shovnng the rays from the microscope and from the drawing sur- face, and the position of the pupil of the eye. For full explanation see Fig. § 182. Arrangement of the Camera Lucida Prism.—In plac- ing this camera lucida over the ocular for drawing or the determination of magnification, the center of the hole in the silvered surface is placed in the optic axis of the microscope. This is done by properly arrang- ing the centering screws that clamp the camera to the microscope tube or ocular. The perforation in the silvered surface must also be at the level of the eye-point. In other words the prism must be so arranged vertically and horizontally that the hole in the silvered surface will be in the axis of the microscope and coincident with the eye-point of the ocular. If it is above or below, or to one side of the eye-point, part or all of the field of the microscope will be cut off. As stated above, the centering screws are for the proper horizontal arrangement of the prism. The prism is set at the rig
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