ii4 



DRA WING WITH THE MICROSCOPE. [CH. V. 



Fig. ioS. Fig. 107. 



Fig. 106. 



Fig 109. 



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



Fig. 106. The Abbe Camera Lucida with 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 of 3$°. 



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 drawing board to 

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

 reflected at 35° must make an angle of no° with a horizontal drawing board. The 

 board must then be elevated toward 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. 108. Upper view of the prism of the camera lucida. A considerable portion 

 of the face of the prism is covered, and the opening in 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 always at 43°, 40°, or 33°, 

 only those angles are shown. 



