CH. VI] DRAWING WITH A CAMERA LUCIDA 161 



(1) Freehand drawings. This is the simplest method if one has 

 natural ability and adequate training, for one only needs an object, 

 pencil, pen and paper. 



(2) Camera lucida drawings. By this method the outlines and 

 proportions can be accurately traced ( 268-275). 



(3) Camera obscura drawings. By this method the real image 

 obtained in a photographic camera can be traced ( 285). 



(4) Projection drawings. In this method real images like those 

 of the magic lantern and projection microscope can be traced directly 

 upon the drawing paper ( 292). 



(5) Line drawings on blue prints and on the back of photo- 

 graphs ( 288-289). 



In many laboratories all the methods are used, sometimes separately, 

 but more often combined. 



267. Free-hand drawings. Microscopic objects may be drawn 

 free-hand directly from the microscope, but in this way a picture 

 giving only the general appearance and relations of parts is obtained. 

 For pictures which shall have all the parts of the object in true pro- 

 portions and relations, it is necessary to obtain an exact outline of 

 the image of the object, and to locate in this outline all the principal 

 details of structure. It is then possible to complete the picture free- 

 hand from the appearance of the object under the microscope. 



268. Camera lucida. This is an optical apparatus for enabling 

 one to see objects in greatly different situations as if in one field of 

 vision, and with the same eye. In other words, it is an optical device 

 for superimposing or combining two fields of view in one eye. 



As applied to the microscope, it causes the magnified virtual image 

 of the object under the microscope to appear as if projected upon the 

 table or drawing board, where it is visible with the drawing paper, 

 pencil, dividers, etc., by the same eye, and in the same field of vision. 

 The microscopic image appears like a picture on the drawing paper 

 (see 27ia). This is accomplished in two distinct ways: 



(i) By a camera lucida reflecting the rays from the microscope 

 so that their direction when they reach the eye coincides with that 

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

 camera lucidas from this group (Wollaston's, fig. 99), the rays are 



