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The relations cos0 =cosy cos Y/2 and cos20 =cosy cos :r for the equi-inclination and normal incidence cases, respectively, have been used in deriving these expressions.Whittaker (1953) has given an expression for P in generally inclined-beam Weissenberg geometry without stating the orientation of the instrumental axis to which it applies. We find that it is equivalent to our expressions for a--~/2. Bond (1959) has recently given the reduction of Whittaker's expression for equi-inclination geometry and has combined this factor with the Lorentz correction.For a given level in the normal incidence method, the angle @ takes values in the range ~ to a + (~/2) --v as :/" ranges from 0 to ~/2. A contrary statement by Azaroff (1955) that in this method @ is equal to v, constant for a given level, is evidently in error.In the case of the precession method, Azaroff (1955) has pointed out that both @ and 2 0s are related in a simple way to co-ordinates on the film. The polarization factor is then easily obtained from his original expression. References (Received 2 June 1959 and inBoron has long been known to exist in several polymorphic modifications, but the systematic study of the structures of these polymorphs was not begun until relatively recently. Hoard et al. (1958) revised form 8 October 1959) a=5.057 /~ and a=58 ° 4'. This cell contains only 12 atoms; the dimensions of the hexagonal cell to which it can be referred are: a=4.908 and c= 12.567 A.All three polymorphs mentioned above have been studied by single crystal methods. Several additional modifications have been reported, based on studies of polycrystalline specimens (Naray-Szabo & Tobias, 1949;Langrenaudie, 1954;Rollier, 1953;Laubengayer et al. 1943).Recently, still another polymorphs was detected in our laboratories.~ Specimens were prepared by the t The specimen was prepared by one of us (C.T.) at Experiment Inc. Richmond, Va.; X-ray studies were carried out at the Polytechnic Institute of Brooklyn.