206 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1952 



of these early systems utilized an attendant on the train. The cost of providing 

 an attendant lias, in some cases, been found excessive. Consequently, experi- 

 ments have been initiated in which a coin box is used on the train. The arrange- 

 ments for this purpose are also described. 



The Magneto-Resistance Effect in Oriented Single Crystals of Ger- 

 manium* G. L. Pearson^ and H. SuhlK Phys. Rev., 83, pp. 768-776, 

 Aug. 15, 1951. 



This paper describes an extensive study of the magneto-resistance effect in 

 germanium as a function of crystal orientation. Experimental measurements 

 establish the constants involved in the dependence of the effect on orientation 

 of magnetic field and electric relative to the crystal axes. The measurements 

 are internally consistent with existing phenomenological theory based on cubic 

 crystal symmetry, in which terms involving the magnetic field to higher than 

 the second order are neglected. It is shown that such deviations as do occur 

 arise from higher terms in the field, since an extension of the phenomenological 

 theory to the fourth order predicts their symmetrj-. Relations are established 

 between the experimentally observed phenomenological constants and those 

 constants appearing in existing magneto-resistance electronic theories. It is con- 

 cluded that no electronic theory yet worked out is entirely consistent with 

 experiment. The present electronic theories are special cases of a verj'- general 

 theory recently proposed by Shockley, and it is possible that agreement can 

 be obtained as soon as the computational difficulties of the latter theory are 

 overcome. 



New Phenomena of Electronic Conduction in Semi-Conductors. W. 

 Shockley^ Semi-Conducting Materials, H. K. Henisch, ed., pp. 26-36. 

 Proceedings of a conference held at the University of Reading (July 

 10-15, 1950) London, Butterworths, 1951. 



The semi-conductors silicon and germanium may be discussed as insulators 

 the electronic structure of which is disturbed. Excess electrons, which act as 

 negatively charged current carriers, may be present as may be 'holes' or places 

 where electrons are missing from the valence-bond structure. Holes act as 

 positively charged current carriers. In ordinary electronic conduction the flow 

 of current carriers is substantially incompressible so that the density of carriers 

 remains constant. Wlien a new transistor phenomenon known as 'carrier injec- 

 tion' occurs, however, the total density of holes and electrons may be greatly 

 increased and this modulation of the electronic structure may be used both for 

 scientific investigation and for practical amplification. In particular, carriers 

 may be injected at a predetermined time and place into a known uniform elec- 

 tric field and their transit time to another place accurately timed by detecting 

 their arrival with a "collector" point. Drift velocities and mobilities may be 

 measured precisely in this way with a directness unattainable by pre-transistor 



* A reprint of this article maj- be obtained on request. 

 1 Bell Tel. Labs. 



