CHAPTER XVII 

 DRAWING 



Use of the Abbe Camera. — A camera lucida drawing 

 might well be made of every microscopical object photo- 

 graphed, since this supplements the photograph by showing 

 different depths. A book of microscopical drawings might 

 be nearly as instructive as a collection of slides, and can 

 be examined more quickly. 



Abbe's drawing camera lucida is doubtless one of the 

 best instruments for drawing objects under the microscope. 

 It needs practice, however, to attain facihty and comfort in 

 its use. Ease of drawing depends, in the writer's experience, 

 on the following points: 



1. The eyepieces used should have a high eyepoint, 

 such as the higher Huyghenian oculars do not possess; so 

 compensating eyepieces are to be preferred. 



2. The exit pupil (eyepiece circle) must be brought into 

 coincidence with the middle of the aperture in the silvered 

 surface of the small prism, both laterally and vertically, 

 the latter being determined by the absence, or small 

 amount, of parallactic shifting when the aperture in the 

 prism is observed directly and obliquely under a lens 

 magnifying 3 or more times. The horizontal adjustments 

 are made by screws; and the vertical adjustment is then 

 done by raising or lowering the apparatus on the tube, 

 after loosening the collar slightly (or, in the new form, by 

 turning a screw). The omission of this vertical adjust- 

 ment is probably the chief cause of difficulty and dis- 

 comfort in drawing. This camera should be used with a 

 small drawing board on the right of the microscope, the 

 board having two triangular supports, slanting it at about 

 35 degrees. The microscope stage is to be adjusted to the 

 same slant. The disc of neutral glasses under the prism 



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