The new graphic method of indexing Debye-Scherrer photographs has been extended to orthorhombic and monoclinic crystals. Line coordinates are amply utilized. Thus the condition that the solution of a series of Diophantine simultaneous linear equations is represented by the interception of a series of conditional lines is replaced by a series of conditional points that passes through a common straight line, the reciprocal intercepts of which on the coordinate axes represent the common solution.Only special cases have been considered. For the orthorhombic system, it is supposed that among the observed lines, there exists a series of reflexions belonging to(1)(hi,0,0),(0,ki,0),(0,0,li);(2)(hi,ki,0),(0,ki,li),(hi,0,li);(3)(hi,k,l), (h,ki,l),(h,k,li) or (4)(hi,ki,l),(h,ki,li),(hi,k,li). And for the monoclinic system, it is supposed that there exists a series of reflexions belonging to (l)(hi,0,0,0),(0,ki,0),(0, 0,li);(2) (hi,ki,0), (0,ki,li); (3) (h,ki,l); (4) (hi,k,l), (h,k,li) or (5) (hi,ki, li)(hi,ki,li),(hi,ki,li),(hi,ki,li). Here the index without a subscript indicates that it remains unchanged in the family of reflexions.A novel feature in this work is that the concept of quadratic difference △isn2θij = sin2θj-sin2θi has been introduced into the graphic method. Thus if there is a set of reflexions in the monoclinic system belonging to the family (hi, k, l), and if we plot (△h2ij/△sin2θij, l△hji/△sin2θij) as conditional points, and if there exists a straight line connecting three or more conditional points arising from different △sin2θij then the reciprocal intercepts of the straight line on the coordinate axes will give A2 and 2AC cosβ, where A=λ/2a sinβ and C=λ/2c sinβ.
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