RECENT ADVANCES IN SCIENCE 195 



analogous to chemical ones do not exist, the configuration of 

 the atoms in the crystals of an ortho-compound may be such 

 that, on fusion, the rearrangement involving the minimum 

 energy change may be such as to give the ortho-compound in 

 the liquid state as well. A general account of the X-ray 

 methods of exploring crystal structure is given by R. Gross 

 {Jahrb. Radioakt. Eledr., 15, 305, 191 8), while papers on the 

 utility of the Laue radiogram, especially as a supplement to the 

 results obtained by Bragg's method, by H. Seeman {Phys. 

 Zeitsch., 20, 169, 19 19) and P. NiggH {ibid., 19, 225, 191 8), have 

 also appeared. 



The investigations in this direction are now tending to go 

 beyond the mere determination of the relative location of the 

 atoms, and in several recent papers the question of the structure 

 of the atoms is taken into account. P. Debye and P. Scherrer 

 have discussed, both from the mathematical and the physical 

 points of view, the possibihty of the electron rings acting as 

 bonds in such a case as the diamond {ibid., 19, 474, 191 8). If 

 such a possibility exists, the presence of these bonds ought to 

 be detectable by means of X-radiograms, but the fact that the 

 results were negative is in favour of Bragg's original structure. 

 On the basis of the theory that the diffracting power of atoms 

 should vary as the Moseley number, the same authors have 

 endeavoured to determine whether there is ionisation in crystals 

 or not, by calculating the number of electrons connected with 

 each atom. In the case of sodium fluoride, the derivation of 

 the number of electrons from measurements of the intensity of 

 reflection from planes composed of a single type of atom suggests 

 that such ionisation exists (cf. D. Coster, Proc. Akad. Amsterdam, 

 22, 536, 1920; H. Thirring, Phys. Zeit., 21, 281, 1920). The 

 suggestion that the influence of the electrons must be taken 

 into account in considering the ultimate structure of crystals 

 has already been made, on theoretical grounds, by F. Rinne 

 {Neues Jahrb. Min., ii, 47, igi6). 



The influence of the electrons is also discussed in a series of 

 papers by M. Born and A. Lande. In the first paper (M. Born, 

 Verh. deut. phys. Ges., 20, 224, 191 8), the absolute crystal 

 dimensions are calculated mathematically on the assumption 

 that the lattice is composed of electronic ring systems such as 

 those postulated by Bohr. In this way the lattice constants 

 of cubic crystals of the sodium chloride type are derived (cf. 

 M. Born and A. Lande, Ber. preuss. Akad. Wiss., 45, 1048, 191 8). 

 From these constants the same authors {Verh. deut. phys. Ges., 

 20, 202, 210, 191 8) calculate the compressibility of the crystal, 

 and find the theoretical value to be twice the observed value. 

 Hence they conclude that atomic structures are three-dimen- 

 sional, and that the plane electronic system is not satisfactory. 



