142 



DRA WING WITH THE MICROSCOPE 



[CH. V 



of the rays from the drawing paper, pencil, etc. In some of the 

 camera lucidas from this group (Wollaston's, Figs. 108, 112), the 

 rays are reflected twice, and the image appears as when looking 



E.P.Y--Y 



■1 



ll 



rlr^- 



<**% 



Fig. 126 



Fig. 124. Abbe Camera Lucida 

 with the mirror at 45°, the drawing 

 surface horizontal, and the micro- 

 scope vertical. 



Axis, Axis. Axial ray from the 



microscope and from the drawing 



surface. A, B. ' Marginal rays of 



Fig. 124 the field on the drawing surface, a b. 



Sectional view of the silvered surface 



on the upper of the triangular prisms composing the cubical prism (P). The 



silvered surface is shown as incomplete in the center, thus giving passage to 



the rays from the microscope. 



Fool. Foot or base of the microscope. 



G. ' Smoked glass seen in section. It is placed between the mirror and the 

 prism to reduce the light from the drawing surface. 



Mirror. The mirror of the camera lucida. A Quadrant (Q) has been 

 added to indicate the angle of inclination of the mirror, which in this case is 



45°- 



Ocular. Ocular of the microscope over which the prism of the camera 

 lucida is placed. 



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



Fig. 125. Geometrical figure showing the angles made by the axial ray 

 with the drawing surface aud the mirror. 



A, B. The drawing surface. 



Fig. r26. Ocular showing eye-point, E. P. It is at this point both hor- 

 izontally and vertically that the hole in the silvered surface should be placed 

 (.1203). 



