94. In =Abbe's Drawing Apparatus= the drawing field is reflected by a mirror at the side of the instrument and by a prism which fits over the eye-piece of the microscope. The prism is supported on a vertical hinge so that it may be readily turned out of the axis of the microscope without disconnecting the whole apparatus from the stand. It is shown turned to the side in the figure. A cylindrical cap accompanies the apparatus which fits over the prism holder and has six lateral windows in which are smoked glasses of various intensity, serving to regulate the lightness of the reflected drawing field =12.--= [Illustration: Drawing Board No. 95. Drawing Board after Giesenhagen.] The =Drawing boards= serve two purposes. They afford a smooth plane surface for the drawing paper and they are so arranged that they may be inclined at such an angle as to receive the rays of the reflected image at right angle to their surface, thus doing away with any distortion of the image on the paper. 95. This =drawing board= is especially adapted for use with drawing eye-piece No. 92. When in the position indicated in the figure its drawing surface forms an angle of 12° to the horizontal =2.--= 96. In =Giesenhagen's drawing board= the drawing surface may be adjusted at various angles and may be raised and lowered =4.--= For drawing eye-piece No. 93 and the Abbe drawing apparatus the surface of the drawing board should be horizontal. [Illustration: Drawing apparatus after v. Tubeuf.] 97. The =drawing apparatus= after v. Tubeuf serves for drawing objects from nature. By means of a prism mounted in a metal box, the object is reflected into the eye in such a manner that its image appears erected on the drawing surface. This is quite an advantage when drawing from nature but is unimportant when using a drawing apparatus on the microscope. Two smoked glasses mounted in moveable metal arms serve to moderate the intensity of the light. On the side of the prism nearest the eye is a small wheel diaphragm attached to regulate the size of the opening. The apparatus is mounted on a heavy nickel-plated stand with vertical and lateral adjustments controlled by thumb-screws =12.--= =Mechanical Stages.= [Illustration: Mechanical stage No. 98.]