147 



the R on t gen-radiation and created the possibility of studying 

 the internal arrangement of the crystalline substances. 



It proved not only the analogy between the nature of the R on t gen- 

 radiation and the wave-motion of ordinary light, and made the 

 determination of its wave-length possible, but it brought simul- 

 taneously the direct proof of the correctness of the ideas which 

 crystallographers had already held for so long about the space- 

 lattice-arrangement of the particles in the crystal. 



Indeed, Von Laue showed that the problem could be attacked 

 succesfully on the basis of the ordinary diffraction-theory, the 

 analytical treatment being, however, appreciably more complicated, 

 because of the tridimensional nature of the grating employed 1 ). 



22. For our purpose it is better, however, not to consider these 

 views in detail here, but to adopt an explanation of the phenomenon 

 brought forward by W. L. and W. H. Bragg, which enables the 

 questions considered here to be treated in a simple geometrical way 



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 207, (1915); Centralblatt f. Miner. (1917), p. 313; Vierteljahrschrift d. Naturf. Ges. 

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 and J. A. Bijl, Proceed. Kon. Akad. van Wet. Amsterdam, 19, (1917); Phys. Zeits., 

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J ) About the application of L a u e-diagrams to problems concerning crystal- 

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