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Zusammenfassung Vor kurzer Zeit wurden Methoden beschrieben nach welchen man rez. Netzebenen eines Kristalles mittels Rontgenstrahlen photographieren kann 1) . Es wurde behauptet dass die Intensitaten mit denen die Punkte aufgenommen werden, ohne Weiteres unter einander vergleichbar sind, weil die von den sekundaren Strahlen durchlaufenen Strecken gleich sind und diese Strahlen unter gleichen Winkeln den Film treffen. Man muss jedoch immerhin den Lorentzfaktor beachten. Dieser wird im Text allgemein fur Drehkristallaufnahmen abgeleitet; er lasst sich fur die genannten Methoden einfach gestalten. Ein Spektrograph zum Photographieren der nullten rez. Netzebene (Aequatorebene) wird beschrieben.

Summary A simple and exact formula for the breadth of Debye Scherrer lines is derived, with the assumption that the crystals have the same form and volume. This formula is used to evaluate the integral breadth as a function of the direction of the normal on the reflecting plane for some triclinic crystals. This leads to a partial justification of the Laue formula, at least for those crystals, which approximate an ellipsoid. It is shown that the value of the constant is 1. For a parallelopipedum another formula is given, so it might be possible to distinguish between these two cases. The volume of the crystals may be found from the half intensity breadth with a greater accuracy than from the integral breadth.

Zusammenfassung Die fruher beschriebene Methode 1 ) wird erweitert, wodurch einige Nachteile aufgehoben werden.

Summary A method is described for obtaining an image of the zero-order reciprocal net plane without any distortion of the picture. This may be important, as all rays reflected by the crystal travel to the film along paths of equal length. Apart from the fact, that they reach the film at a constant angle, which can be adjusted so as to suit any special demands, the intermediate distances between the reciprocal net points on the photography can also be varied. These features render the method useful for the comparison of intensities. For research work on fibres it may also be of some use.

Summary The diffuse streaks, appearing on a Laue photograph of tin, which have been previously discussed, are now considered in the light of the thermal theory of diffuse spots. The calculation, starting from the elastic constants of tin, shows a rather good agreement with the observed diffuse streaks. A small discrepancy may indicate that the assumed value for at least one of the constants is wrong.

A general theory of waves, irrespective of their physical properties, is expounded. Only non-absorbing media are considered. Next to the Snellius laws, which follow from the general aspects of waves, three principles are needed. From these the intensity of reflection may be found and the connection between scattering, the refractive index and the energy transport by the wave. The two formula's of Fresnel are closely connected with two kinds of scattering, the first one with isotropic scattering, the second formula with dipole scattering. Differential equations are not used. The general theory is applied to sound, light and X-rays and to electron waves.