( 715 ) 



Wien's experiments would have led to results more in keeping 

 with the diffraction experiments, if' the values found for the energy 

 of the R.-rays had heen 20 to 100 times smaller. The difference is 

 too great to ascribe it to errors of observation. We must rather 

 think of' fundamental errors in the method of' observation or of a 

 viciousness in our conceptions concerning the mechanism of the 

 phenomena. 



As for the method of observation Wikn himself' pointed out 1 ) 

 the possibility that the quantity of heat, generated in the bolometer 

 or in the thermo-element, should not be to its full amount converted 

 energy of R.-rays, but partly also — perhaps even for the greater 

 part — converted atom-energy, liberated by a, say, catalytic action 

 of the R.-rays. 



J. D. v. d. Waals Jr. 2 ) suggests the additional idea that the 

 electrons are not generally stopped at once by a simple uniform 

 decrease of velocity, but will mostly, by their interacting with the 

 particles of' the anti-cathode, before being brought to rest move for 

 some time amidst the latter in rapidly changing directions with great 

 velocities, sending out a new R. -pulse at every change of motion. 

 Starting from this idea we could, indeed, expect from each electron 

 a much greater contribution to the energy of radiation than in 

 the theory accepted by Wien and find the results of Wien's energy- 

 measurements in better agreement with those of the diffraction- 

 experiments. 



Nevertheless it seems to me that by the side of this another idea 

 deserves our attention, which might be more in keeping with the 

 properties of cathode-rays as far as known. It would be this, that 

 not simply the cathode-ray electrons, but in combination with these 

 the atoms of the anti-cathode are the principal centres of emission 

 of R.-rays. 



It should be imagined, that the electrons, arriving at the antieathode 

 with their immense velocities, are not, generally, thrown into an other 

 direction by the atoms, but will for the greater part pass straight through 

 them, and even, in doing so, will mostly not suffer any persisting 

 decrease of velocity. This idea is by no means a new one. It has 

 been worked out by Lenard a ), who sees in it the best explanation 

 for the laws of absorption of the cathode-rays. In very few cases only 

 it will happen that an electron, when piercing an atom, gets imprisoned 



i) W. Wien. Drudes Ann. d. Ph. 18, p. 1005, 1905; cf. also E. Gabter. Ann. 

 d. Ph. 21, p. 957, 1906. 



2) J. D. v. d. Waals Jr. Ann. d. Ph. 22. p. 603. 1907. 

 ••) P. Lenard. Drudes Ann. d. Ph. 12, p. 734, 1903. 



49 

 Proceedings Royal Acad. Amsterdam. Vol. IX. 



