ABSTRACTS OF TECHNICAL ARTICLES 185 



spots made up of three distinct patterns which are displaced with 

 respect to each other and with respect to the primary beam position. 

 PolycrystaUine surfaces made up of rather large crystals produce 

 patterns of spots which are often drawn out into streaks lying ap- 

 proximately parallel to the plane of incidence. This effect, which is 

 attributable to refraction and is a proof of smoothness of the surface, is 

 most pronounced after etching in nitric acid. It is rarely, or never, 

 found after etching in a mixture of hydrogen peroxide and ammonium 

 hydroxide. Nitric acid etch produces upon the surface of a single 

 crystal of cuprous oxide, or upon a polycrystalline surface made up of 

 rather large crystals, crystals of some new compound which are cubic 

 with cell edge 8.35A. These are sharply oriented with one or another 

 of the most important planes parallel to the gross surface plane of the 

 oxide. The sharpness of this orientation is proof of the flatness of the 

 underlying oxide surface upon which the crystals are formed. This 

 new 8.35A structure is produced by potassium cyanide etch as well as 

 nitric acid, but never by sulphuric acid nor by ammonium hydroxide. 



On the Ionization of the Ft Region."^ W. M. Goodall. In this paper 

 the available data on F2 region ionization for Peru, Australia, and this 

 country are analyzed in a way that permits the separation of effects 

 due to variations in solar ionizing force from effects due to seasonal 

 and annual changes. It is shown that for constant solar activity the 

 expected curves of critical frequency for Australia and this country 

 appear to indicate both seasonal and annual tendencies. It is sug- 

 gested as a possibility that the apparent "annual" effect may in fact 

 be due to meteorological conditions which cannot be eliminated with- 

 out data from more locations. 



Coupling Between Parallel Earth-Return Circuits Under D-C Transient 

 Conditions.^ K. E. Gould. In tests conducted in connection with 

 several d-c railway electrifications, the induced voltages recorded in 

 paralleling communication circuits at times of short circuit on the 

 railway have shown marked divergences from values computed on the 

 basis of uniform earth resistivity and a rate of change of earth current 

 determined from measurements in trolley and rail circuits. Due to 

 the numerous factors which might contribute to these divergences, 

 such as non-uniform division of transient current along the tracks and 

 associated return conductors, the presence of shielding conductors 

 along or near the right-of-way, etc., it was felt that a better under- 

 standing of the problem of induction under d-c transient conditions 



4 Proc. I. R. E., November 1937. 

 ^ Elec. Engg., September 1937. 



