i 4 8 DRAWING WITH THE MICROSCOPE [CH. V 



Fig. 129 



Abbe Camera Lucida in position to avoid distortion. 



Fig. 129. 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 o/_j5°> 



Ocular. Ocular of the Microscope. 



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



W. Wedge to support the drawing board. 



A. 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°' makes an angle of 110° 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 fulfil the requirements neces- 

 sary to avoid distortion ( $ 200, 204) . 



B. Upper view of the prism of the camera lucida. A considerable por- 

 tion of the face of the prism is covered, and the opening in the silvered surface 

 appears oval. 



C. 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 45 , 40° or 

 35° , only those angles are shown. 



