432 
of both phenomena in ammonium-chloride may not be considered 
however as a statement of these results. For Vorer') finds the 
connexion 
ar GM bt EERE 2 
NA, — NK 
where nz is the absorption coefficient outside the field, m,z, and 
n‚x, the absorption coefficients for the ordinary and the extraordinary 
rays. For ammonium-chloride it has been found here however, that 
the vibrations along both of the principal directions are absorbed 
stronger, so that the above fraction is positive. | 
A plausible representation of these phenomena may be obtained 
however by the assumption of an orientation of the somewhat 
elongated particles of the ammonium-chloride. 
The phenomena of Case I (see 9) are analogous to phenomena of 
this kind: fine lines on glass or corrosion figures on crystals are seen 
clearly, when the length direction of the lines or figures is perpen- 
dicular to the plane through the incident ray and the line of 
observation ®). In Case II the eye has the most disadvantageous 
position to receive light of the orientated particles. In Case IV the 
incident light has a disadvantageous direction for the deflexion. 
vase V is easily derived from IV. The dispersion only cannot be 
explained by the orientation. For in the case of a slit-width below 
a wavelength we should expect just the opposite from what has 
been observed. 
Finally I-wish to express my indebtedness to Prof. Zeeman for 
his encouragement and powerful assistance in this research. 
Amsterdam, June 1916. 
Chemistry. — “The Interpretation of the Röntgenograms and 
töntgenspectra of Crystals”. By Pror. A. Smrrs and Dr. F. E. 
C. SCHEFFER. (Communicated by Prof. J. D. van Der Waats). 
(Communicated in the Meeting of June 24, 1916.) 
|. Lave’s researches *) and those by W. H. and W. L. Brace *) 
about the diffraction of Röntgenrays by crystals have given rise 
to a view about the arrangement of the atoms in the solid substance, 
which, though sufficiently in agreement with the physical properties 
of the substanee, cannot be reconciled with our chemical ideas. 
1) Loe. cit. p. 588. 
2) Compare Corron et Movron, Les ultramicroscopes, les objets ultramieros- 
copiques. Paris 1906, p. 167. 
3) Sitzungsber. d. Bayer. Akad. d. Wiss., Juni 1912. 
4) Proc. Cambridge Phil. Soc. 17 (1912) I, 45 
