CH. XI] MODELS FROM SERIAL SECTIONS 415 



section and with the projection microscope throw the image on the 

 table (fig. 246). By using different objectives and different distances 

 from the microscope one can find a size which seems suitable. The 

 magnification may be found by 276. Then by multiplying the whole 

 number of sections by the thickness of the sections and this by the 

 magnification', one can get the length or height of the model. One 

 must take these preliminary steps and decide upon the magnification 

 to be used or the model is liable to be too large to be manageable or 

 too small to show well the necessary detail. 



(1) Suppose the model is to be 100 times the size of the original 

 object, and the object has been cut into a series of sections IOJJL thick. 

 Then each section must be represented by a plate or sheet 100 times 

 as long, broad, and thick as the object. As the sheets of blotting 

 paper are so large (61 X 48 cm.), one need be solicitous only about 

 the thickness. 



As each section is actually IOJJL thick and the model is to be 100 

 times enlarged, the thickness representing each section must be 

 ioju X ioo = loooju, or i millimeter, i millimeter blotting paper is 

 used and every section of the series is drawn. 



(2) If the blotting paper were only fV mm. thick it would be 

 simpler to make the model 90 times the size of the original. If, how- 

 ever, one wished the magnification to be ioo, it could be accomplished 

 thus: Each section in the series should be represented by i mm. or 

 loooju in thickness. But if one uses blotting paper of & mm. thick- 

 ness or 9ooju, there is a loss of ioo/i for each section and for 9 sections 

 there would be a loss of 900/1, or the thickness of a sheet of the blotting 

 paper. To remedy this one uses 10 sheets of blotting paper for 9 

 sections. This keeps the model in true proportion. In practice each 

 of the sections is drawn upon one sheet except one of them and for 

 that two sheets of the blotting paper are united and the sections 

 drawn upon the double sheet. 



671. General rule for the use of blotting paper. Divide the 

 thickness by which each section is to be represented in the model by 

 the thickness of one sheet of the blotting paper available. The quo- 

 tient shows the number of sheets or the fraction of a sheet required 

 for each section. 



