CH. V] 



DRA WING WITH THE MICROSCOPE 



123 



inversion is a great objection, as it is necessary to similarly invert all 

 the details added free-hand. 



(B) By a camera lucida reflecting the rays of light from the draw- 

 ing paper, etc. , so that their direction when they reach the eye coin- 

 cides with the direction of the rays from the microscope (Fig. 58, 109). 

 In all of the camera lucidas of this group, the rays from the paper are 

 twice reflected and no inversion appears. 



Fig. 109. 



Fig. hi. 



Fig. 109. Abbe Camera Lucida with 

 the mirror at 45 , the drawing surface 

 horizontal, and the microscope vertical. 



Axis, Axis. Axial ray from the mi- 

 croscope and from the drawing surface. 

 A, B. Marginal rays of the field on the 

 drawing surface, ab. Sectional view of 

 the silvered surface on the upper of the tri- 

 angular 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. 

 Foot. 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 i?i this case is 45°. 



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

 is placed. 



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

 Fig. 1 10. Geometrical figure showing the angles made by the axial ray with 

 the drawing stirface and the mirror. 

 A, B. The drawing surface. 



Fig. hi. Ocular showing eye-point, E. P. It is at this point both horizontally 

 and vertically that the hole in the silvered surface should be placed (| 182). 



