Pomona College, Claremont, California 



75 



diagramatic illustration of the reconstruction oi one cylinder inside 

 another by means o! this method. 



The sections are cut at right angles to the orientation plane and 

 hence transversely to the axis oi the object. I he knife must be 

 sharp and care must be taken in the mounting to prevent any warp- 

 ing or wrinkling ol the sections. An outline ol the first section is 

 drawn by means of a projection lantern— represented by the shaded 

 circles ( Pig. 14; a) — and a line drawn on the projection ol the edge 

 of the section of the liver-piece, represented by the first cross line on 

 b ( Fig. 14). From the ends of this cross line are drawn lines in that 

 direction from the cross line that is related to the cross line in the 

 same way as the side ol the drawing, which is a projection ol pari 

 of the aspect to be reconstructed, is related to the center ol the 

 drawing. These two lines (the long parallel lines, Fig. 14; b), 

 determine the projection ol the orientation plane, ami on them 

 are measured oft segments about equal to half of the product of 

 the thickness of the sections times the magnification in diameters. 

 The projection of the second section of the series is so placed that 

 the projection of the edge of the liver section coincides with a 

 line drawn between the dots marking ott the first segment on the 

 lines determining the orientation plane. I lie section itself is out- 

 lined in the same way except that those parts of the second out- 

 line which are "covered up" or are within the area bounded by 

 the first outline are left blank, since they represent the parts ol 

 the surface which arc hidden from view by the outcurving nearer 

 surfaces. The process is repeated progressively along the seg- 

 ments oi the displacement lines with all ol the rest of the sec- 

 tions. Those lines which form the edges ol the completed figure 

 are re-enforced and then transferred to a separate sheet of paper. 

 This bare outline is shaded to till out the contour ol which the 

 lines on the other sheet arc a topographic diagram as shown (big. 

 14c). 



It is obvious that the cylinder is somewhat distorted since the 

 face of the figure seen from this point of view should be an ellipse 

 The distortion is known as a sheering distortion, but as it is con- 

 stant and does not appreciably alter the relations of the parts the 

 distorted reconstruction is quite as useful as the normal one. 



