4i6 MODELS FROM SERIAL SECTIONS [Cn. XI 



If a quotient is a mixed number reduce it to a fraction. The 

 numerator represents the number of sheets required and the denomi- 

 nator the number of sections to go with the sheets. 



Examples: (a) With a series of loju sections to be modeled at 100 

 enlargement each section of the series must be represented in the 

 model by a thickness of 10/4 x 100 = 1000/4 or i millimeter. If one 

 uses millimeter or IOOOJJL paper, then 1000/4 -f- IOOO/A = -J-, and one 

 must use i sheet for i section. 



(b) With a series of 10/4 sections to be made into a model 100 times 

 enlarged, and with blotting paper of & mm. or 900/4 thickness, each 

 section must be represented by 10/4 x 100 = 1000/4. If the blotting 

 paper is 900/4 thick, then it requires for each section: 1000 -f- 900 = i^ 

 sheets of paper or -^ sheets for one section or 10 sheets for 9 sections, 

 that is a double sheet for one of the nine sections. 



(c) With a series cut 15/4, for a 50 fold model, each section is 

 represented by a thickness of 15/4 X 50 = 750/4. If one uses i mm. 

 or looo/t blotting paper, then each section requires 750 -f- 1000/4 = J 

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

 omits every fourth section in drawing, thus: ist, 2d, and 3d sections 

 would be drawn; then the 5th, 6th and 7th; gth, loth, nth, etc., 

 every fourth being omitted. 



(d) If for the model just considered one had y 9 <j mm. or 900/4 paper 

 then 750 -i- 900 = f . 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). 



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 pro- 

 duce 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). 



DRAWINGS FOR MODELS 



672. The methods given for drawing microscopic preparations 

 in Ch. VI are all applicable except the freehand method. This is not 

 applicable, because it is not possible to draw at a uniform and accurate 

 enlargement in that way. But the camera lucida method ( 275) 



