372 SCIENCE PROGRESS 



structure be entirely unknown. The system is peculiar to itself, 

 and, if found in the photograph of any material, the substance 

 must be present. There is no ambiguity, as the whole system 

 of each substance present in quantity must be reproduced intact, 

 and the probability of even one or two Hues being the same for 

 different materials is very small. In cases of doubt or of cornplex 

 mixtures, shorter or longer wave-lengths may be used giving 

 correspondingly complex or simple spectra. The determination 

 is even roughly quantitative, but its main value lies in showing 

 the actual state of combination and in the small quantity of 

 the substance necessary. 



Several other practical applications suggest themselves 

 along these lines, and the method is hkely to become a 

 permanent institution when refinements of apparatus allow 

 greater economy in the taking of exposures. 



The appended list includes the principal papers which have 

 been published dealing with this method and the results 

 obtained by it : 



Debye and Scherrer, Physik. Zeitsch., xvii. p. 277 (1916); 

 xviii. p. 291 (1917) ; xix. p. 474 (1918). 



Johnson and Toeplitz, Physik. Zeitsch. y xix. p. 47 (191 8). 



H. Bohlin, Ann. der Physik., 5, 61 (1920). 



A. W. Hull, Phys. Rev., x. 661 (1917)- 



Journ. Amer. Chem. Soc, August 19 19. 

 Collected with other papers in " X-ray Studies," Gen. Elect. Coy., 



N.Y., 1919- 



The Magnetic Properties of Crystals. — Oxley has extended 

 his researches on magnetism and atomic structure (cf. " The 

 Relation of Magnetism to the Crystalhne State," Science 

 Progress, April 1920, a summary of his previous work) 

 by the investigation of the deportment of naphthalene crystals 

 and other substances in the magnetic field. From these results, 

 and those of Tyndall, it is seen that we must admit a special 

 distribution of electron orbits in the atom in order to account 

 for magnetic deportment and crystalHne structure. It is found 

 that the aggregate projected area of such orbits, on a plane 

 perpendicular to the principal cleavage, is a maximum both for 

 diamagnetic and paramagnetic crystals. This conclusion is not 

 inconsistent with the Lewis-Langmuir theory on which pairs 

 of electrons are held in common. Oxley attributes the rigidity 

 of crystalline elements and non-conducting compounds to 

 highly localised magnetic doublets, such as would exist if the 

 electron itself were magnetic. These determine the orientation 

 of the molecules of the space lattice. The Laplace intrinsic 

 pressure is due to the more open electrostatic doublets, the 

 mechanical stress arising from these having a definite mean 

 value whatever the molecular orientation. 



