Pomona College, Claremont, California 75 



diagramatic illustration of the reconstruction of one cylinder inside 

 another by means of this method. 



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

 hence transversely to the axis of the object. The knife must be 

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

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

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

 circles (Fig. 14; a)^and a line drawn on the projection of 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 of the drawing, which is a projection of part 

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

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

 determine the projection of the orientation plane, and on them 

 are measured off 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 off the first segment on the 

 lines determining the orientation plane. The 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 bv 

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

 the surface which are hidden from view by the outcurving nearer 

 surfaces. The process is repeated progressively along the seg- 

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

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

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

 This bare outline is shaded to fill out the contour of which the 

 lines on the other sheet are a topographic diagram as shown (Fig. 

 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. 



