548 BELL SYSTEM TECHNICAL JOURNAL 



The Scattering of Electrons by a Single Crystal of Nickel.^ C. Davis- 

 son and L. H. Germer. Preliminary announcement is made in this 

 note of the discovery that a beam of swiftly moving electrons in its 

 reaction with a single crystal of nickel behaves in some respects as if 

 it were a beam of wave radiation such as light or x-rays. As the speed 

 of the electron beam is increased a series of critical speeds is found 

 at which sharply defined beams of scattered electrons issue from the 

 crystal. This is similar to w^hat is observed when a beam of mono- 

 chromatic x-rays is sent into a crystal — as the wave-length of the 

 x-rays is decreased a series of critical wave-lengths is found at which 

 sharply defined beams of scattered x-rays issue from the crystal. 

 This x-ray phenomenon is quantitatively accounted for as due to the 

 interference of waves scattered by the regularly arranged atoms of 

 the crystal. In fact, it was this phenomenon discovered by Laue, 

 Friedrick and Knipping in 1913 that established the wave nature of 

 x-radiation, and it is from measurements based on this phenomenon 

 that the lengths of x-ray waves are determined. 



The analogous electron phenomenon is less simple, and yet it is 

 simple enough and of such a nature as to leave little doubt that a 

 beam of swiftly moving electrons is in some sense equivalent to a 

 beam of wave radiation. The wave-length of the equivalent radiation 

 can be measured, and is found to be in satisfactory agreement with 

 requirements of the new theory of wave or undulatory mechanics: 

 namely, that the wave-length of the equivalent radiation shall be equal 

 to h/mv, where h represents Planck's universal constant of action, and 

 mv the momentum of an individual electron. 



Structure of a Protective Coating of Iron Oxides J Rich.a.rd M. 

 BozoRTH. It is shown that the Bower-Barff protective coating, pro- 

 duced by the action of steam on iron at about 700° with subsequent 

 cooling in air, is built up of layers of ferrous oxide, magnetite and 

 ferric oxide, arranged in this order (the order of oxidation) upon the 

 iron base. The thicknesses of these layers are estimated to be of the 

 order of 10"-, 2 X 10~^ and 2 X 10~^ cm., respectively. The data 

 on which the above conclusions are based are the positions and intensi- 

 ties of lines on powder photographs taken with molybdenum, iron and 

 copper Ka X-rays. The iron and copper Ka X-rays penetrate the 

 coating to different depths and give information about different parts 

 of its structure because their wave-lengths are, respectively, a little 

 greater and a little less than the critical-absorption w^ave-length of 

 the iron which forms the greater part of the coating. 



6 Nature, 119, 558 (1927). 



' J. Amer. Chem. Soc, \ol. 49, pp. 969-976 (1927). 



