164 



DRAWING WITH A CAMERA LUCIDA 



[CH. VI 



the rays from the microscope, so that the two fields appear as one, and 

 the image is seen as if on the drawing surface (fig. 100-102, 27ia). 



FIG. ioo. DIAGRAM OF ABBE'S CAMERA LUCIDA WITH A VERTICAL MICROSCOPE. 



Axis, Axis The axial ray of the microscope and from the field of the drawing 

 surface. 



Ocular The upper part of the microscope ocular. 



Mirror The mirror of the camera lucida reflecting the rays from the drawing 

 surface at right angles to the axis. 



P, P The drawing pencil in the field, and the prism of the camera lucida. 



Q The quadrant attached to the mirror to give the angle. 



G Smoked glass. 



a b The silvered surface in the prism with a hole made in the center for the 

 light to pass upward from the microscope. The silvered part reflects the rays from 

 the drawing surface. 



The geometrical figure at the left gives the angles when a 45 mirror is used. 



271a. For some persons the image and the drawing surface, pencil, etc., do 

 not appear on the drawing board as stated above, but under the microscope, ac- 

 cording to the general principle that "objects appear in space where they could 

 be touched along a perpendicular to the retinal surface stimulated," that is, in 



