en. -V] 



DRAWINGS FOR MODELS 



329 



of a sheet for one or 3 sheets for 4 sections. In this case one omits 

 every fourth section in drawing, thus : 1st, 2d, and 3d sections 

 would be drawn ; then the 5th, 6th and 7th ; 9th, 10th, nth, etc., 

 every fourth being omitted. 



(d) If for the model just considered one had r 9 ^ mm. or 900/; 

 paper then 750-^-900=4. That is there must be 5 sheets of the 

 paper for each 6 sections. In that case every sixth section would 

 be omitted in the drawing as every fourth section was omitted in (c). 



Fig. 257. Abbe Camera Lucida in connection with Bernhard' s drawing 

 board. The drazving board is adjustable vertically for a greater or less image 

 distance. It may also be elevated toward the microscope to prevent distortion 

 (Fig. f2g). The base board is hinged so that microscope and board may be 

 i?iclined together (Zeiss' Catalog). 



It is of course best to use sheets of exactly the right thickness 

 to represent the necessary thickness in the model, (a) but one can 

 produce models with accuracy by duplicating one or more sheets 

 for a group of sections (b) or by omitting certain sections of the 

 series in drawing (c, d). 



§ 495. Drawings for Models. — For drawing one may use 

 the camera lucida (Figs. 128, 132, 257), taking the precautions to 



