153 



25. The behaviour of the sylvine-crysta]. towards the Ron t gen- 

 radiation can, therefore, easily be explained, when the supposition 

 is made that the 

 radiation observed 

 is produced by par- 

 ticles arranged in a 

 simple cubic space- 

 lattice. Now expe- 

 rience shows that 

 the intensity of the 

 secondary radiation 

 produced by Ront- 

 g en-pulses passing 

 over atoms, is inti- 

 mately connected 

 with their atomic Fig. 126. 



weight; more parti- Structure of Potassium-, and Sodiumchloride. 



cularly it appears 



that the amplitude of the waves reflected by each net-plane is nearly 

 proportional to the total mass of the atoms lying in that net-plane. 

 If the number of particles in two successive netplanes is the same, 

 the ratio of the amplitudes of the waves reflected by them, will 

 therefore be almost the same as that of the individual masses 

 of both net-planes. And because the atomic weights of potassium 

 (= 39) and of chlorine (35,5) are only slightly different, it will be 

 understood that these atoms will behave almost as if the particles 

 arranged in the cubic space-lattice were really all of the same kind. 

 But when sodiumchloride is used in the experiment, experience 

 shows that the character of the reflection at the faces of { 1 00 ] and 

 110} is exactly analogous to that observed at the same faces of 

 the potassium-sa.\t. The reflection at (111), however, manifests an 



