430 APPENDIX ON DRAWING THE 



The directing planes b b'" b*, and b' b" b*, No. 4, 

 represent the 2 planes b^ b'*, No. 5 ; and b b'" b *, 

 I)' b" bz, No. 4, represent #*, which are marked only 

 by the number 2 in No. 5 ; and n % b" 1 s' ? No. 4, is 

 evidently parallel to plane e, No. 5. 



The intersection of b b"' b* 9 with n % b"' s', is the 

 line n b'" ; its intersection with P is b b'"; with M, it 

 is b b i ; and with b' &" 6 1 , it is & m. 



If, therefore, from the point I, No. 5, we draw the 

 line 1 6, parallel to n V", No. 4 ; 6 5, to b b'" ; and 

 13, to b b* 9 we shall obtain three of the edges of 

 plane b*. From the point 5. No. 5, draw the inter- 

 section of b and b' * , parallel to m b i , No. 4 ; and by 

 drawing on No. 5, 3 4, parallel to b b*, No. 4, and 

 the intersection of 2 and a', No. 5, parallel to m b* 9 

 No. 4, we shall delineate the planes Z> and 2 ; ob- 

 serving that those planes intersect each other in a line 

 parallel to the intersection of bi and P. The posi- 

 tions of b'i and 2 may be obtained by a similar 

 method of proceeding, and the other corresponding 

 planes may be drawn by a similar process, or by 

 parallel lines, or by finding the relation of their 

 edges, or angles, to some known points on the 

 crystal. 



We shall give our next illustrative example from 

 the rhomboid. Let us suppose an obtuse rhomboid 

 is to be represented, modified by planes belonging to 

 classes g, ??z 3 o, and p, and whose symbol is 



iDi 2D2 iBi 6 P. 



o p m g P 



