310 BELL SYSTEM TECHNICAL JOURNAL 



which short waves arrive at a receiving site. Data on transatlantic 

 stations are presented to illustrate the use of the methods. The meth- 

 ods described include those in which the phase difference between two 

 points constitutes the criterion of direction, and those in which the 

 difference in output of two antennas having contrasting directional 

 patterns determines the direction. The methods are discussed first 

 as applied to the measurement of a single plane w^ave. Application 

 to the general case in which several fading waves of different directions 

 occur then follows and the difficulties attending this case are discussed. 



Measurements made with equipment responsive to either the hori- 

 zontal or the vertical component of electric field are found to agree. 



The transmission of short pulses instead of a steady carrier wave is 

 discussed as a means of resolving the composite wave into components 

 separated in time. More detailed and significant information can 

 be obtained by this resolving method. The use of pulses indicates 

 that (1) the direction of arrival of the components does not change 

 rapidly, and (2) the components of greater delay arrive at the higher 

 angle above the horizontal. The components are confined mainly to 

 the plane of the great circle path containing the transmitting and 

 receiving stations. 



A method is described in which the angular spread occupied by the 

 several component waves may be measured without the use of pulses. 



Application of highly directional receiving antennas to the problem 

 of improving the quality of radiotelephone circuits is discussed. 



Electron Diffraction and the Imperfection of Crystal Surfaces.^ L. H. 

 Germer. Bragg reflections are obtained by scattering fast electrons 

 (0.05A) from the etched surfaces of metallic single crystals. The 

 surfaces studied are a (100) face of an iron crystal, (111) face of a 

 nickel crystal and (110) face of a tungsten crystal. In each case the 

 reflections occur accurately at the calculated Bragg positions with no 

 displacement due to refraction. A given reflection is found, however, 

 even when the glancing angle of the primary beam differs considerably 

 from the calculated Bragg value — by over 1.0° in some cases — so that 

 several Bragg orders occur simultaneously. The accuracy with which 

 this glancing angle must be adjusted is a measure of the degree of 

 imperfection of the crystal. From the electron experiments, estimates 

 are made of the widths at half maximum of electron rocking curves. 

 These widths are 0.8° for the iron crystal, 1.5° for the nickel crystal 

 and somewhat over 1.0° for the tungsten crystal. X-ray rocking curves 

 for these same crystals are much narrower, although the observed 



^ Phys. Rev., December 15, 1933. 



