WAVES AND CORPUSCLES — DE BROOLIE 253 



The experiments which we liave just described, which appear to 

 liave been lirst nnide by my brother Maurice before the war, are 

 generally known as the experiment of Debye and Scherrer. They 

 prove the wave structure of X rays, but that was already known be- 

 fore these experiments. If now we repeat these experiments with 

 electrons, we would have a proof of the wave character of the elec- 

 tron. This was realized by Messrs. Thomson and Ponte. M. Ponte 

 proceeded as follows: He sent a bundle of electrons upon a film of 

 zinc oxide formed of little crystals of this substance. Then plucinj^ a 

 photographic plate as I have described above he obtained photo- 

 graphs such as are shown in Plate 1, Figure 2. 



The diameter of the rings corresponds to what was foreseen by 

 the fornmlae of wave mechanics. These formulae, we have seen, 

 tell us the wave length associated with the electron which is smaller 

 tlie greater the velocity of the electron. Therefore, if we first send 

 upon the zinc oxide screen electrons having a certain velocity, we 

 obtain a definite system of rings (pi. 2, fig. 1) ; if next we send 

 electrons of greater speed, we obtain a similar system of rings but 

 moved further in towards the center (pi. 2, fig. 2). The corre- 

 spondence with the predictions of wave mechanics is quantitative 

 with an accuracy of at least 1 per cent. 



The experiments of Davisson and Germer, of G. P. Thomson, of 

 Ponte, and of others, have proved that the electron is not a simple 

 corpuscle ; it is at the same time a corpuscle and a wave. It is doubt- 

 less the same case with the proton as all recent experiments seem to 

 prove. As matter seems to be formed of protons and electrons, we 

 see that matter, like light, is made of corpuscles and waves. Matter 

 and light thus appear to be much more similar than we had supposed 

 only a very short time ago when we considered matter as being com- 

 posed of corpuscles only. Undulatory mechanics has thi^s em- 

 bellished and simplified our conception of Nature. Further it has 

 led us to predict interference and diffraction phenomena with elec- 

 trons of which 1 have just shown you the experimental proofs. One 

 can say then that an iin])ortant step has thus been taken along the 

 road which little by little leads the human mind to a more exact 

 knowledge of the secrets of Nature. 



