Particle Shape

Abstract

MR. S. I. TOMKEIEFF'S criticisms of the coefficients I have proposed for expressing particle shape are based on two points: the term 'acicularity' applied to the coefficient ac: b², and the use of a: b or b: c as the second shape parameter. With regard to the definition of acicularity, I would point out that my use of this term is an extension of its common meaning, so that it may be applied in a generalized sense to figures with three unequal principal dimensions. This extension is quite analogous to the extension of the terms positive and negative as applied to the indicatrix of biaxial crystals in crystal optics, these terms being derived from their use in describing the indicatrix of uniaxial crystals. Also, although my isoproportionality coefficient is not an explicit function of all three dimensions, it is not independent of any of their values owing to its definition as a: b, or b: c, whichever is the smaller, and it does, in combination with the acicularity coefficient, uniquely express any shape. Although there is a loss in mathematical rigour here, there is a great gain in simplicity.