by M. W. Porter & R. C. Spiller. -- Published for the Barker Index Committee by W. Heffer, 1951. -- (The Barker index of crystals : a method for the indentification of crystalline substances / by M.W. Porter and R.C. Spiller ; v. 1 . Crystals of the tetragonal, hexagonal, trigonal and orthorhombic systems ; pt. 1).