ii4 



DRA WING WITH THE MICROSCOPE. [CH V. 



Fig. ioS. Fig. 107. 



UL^gfe^^g 



Fig. 106. Fig 109. 



Figs. 106-109. Abbe Camera Lucida in position to avoid distortion. 



Fig. 106. The Abbe Camera Lucida zvith the mirror at 35 . 



Axis, Axis. Axial ray from the microscope and from the drawing surface. 



A B. Drawing; surface raised toward the microscope 20°. 



Foot. The foot or base of the microscope. 



Mirror with quadrant {Q). The mirror is seen to be at an angle ofj^°. 



Ocular. Ocular of the microscope. 



P, P. Drawing pencil, and the cubical prism over the ocular. 



W. Wedge to support the drawing board. 



Fig. 107. Geometrical figure of the preceding, showing the angles made by the 

 axial ray with the mirror and the necessary elevation of the drazving board to 

 avoid distortion. From the equality of opposite angles, the angle of the axial ray 

 reflected at jf° must make an angle of //o° zvith a horizontal drazving board. The 

 board must then be elevated tozvard the microscope 20° in order that the axial ray 

 may be perpendicular to it, and thus fulfill the requirements necessary to avoid dis- 

 tortion ($ 170, 174). 



Fig. ioS. Upper view of the prism of the camera lucida. A considerable pot Hon 

 of the face of the prism is covered, and the opening hi the silvered surface appears 

 oval. 



Fig. 109. Quadrant to be attached to the mirror of the Abbe Camera Lucida to 

 indicate the angle of the mirror. As the angle is nearly alzvays at 45°, 4.0°, or jj°, 

 only those angles are shown. 



