carrying a series of dark glasses of different shades, 

 has centering arrangement to bring the opening of the 

 cube into the optical axis and swings out so that the 

 object can be viewed without disturbing the camera 

 lucida. 



To obtain satisfactory results with any camera 

 lucida several fundamental rules must be observed : 



Use sharp pencil point. If spectacles are necessary 

 o read they must be used with the comer a lucida to see 

 the pencil point. 



The light in the field of view and from the drawing 

 surface should be of about the same intensity. 



The drawing surface should be at right angles to 

 the axis of the projected image, otherwise there will be 

 an elongated picture and distortion at one end. 



Draw the outline of the image and indicate the 



details of structure in light lines and complete the 



drawing without the camera lucida by reference to the 

 microscope. 



Illumination. The relative illumination of the 

 field in the eyepiece and drawing paper varies with the 

 magnifying power and distance of paper from the eye- 

 piece. The control of the illumination in the better 

 class of camera lucidas provided with glass shades is 

 comparatively easy, but in the simple forms several 

 expedients must be resorted to. 



170 



