ABSTRACTS OF TECHNICAL ARTICLES 627 



conductors, since the only discontinuities are those involved in the 

 connection of the conductor to the track; it is also conveniently adapted 

 to modifications for discontinuities. The general single series discon- 

 tinuity is a fundamental point of departure in the treatment of such 

 apparatus as track booster transformers. The basic circuit modified 

 by discontinuities as required gives directly the propulsion circuit 

 impedances needed in the railway network impedance diagram; it 

 may also be employed in the construction of a particular kind of 

 cumulative induction curve for neighboring communication lines, 

 which takes into account the distribution of current along the track. 

 The method of building up complex propulsion systems from basic 

 circuits is illustrated by examples chosen for their practical importance, 

 but the paper does not give detailed procedure for engineering appli- 

 cation of the method and its results. 



Kennelly-Heaviside Layer Studies Employing a Rapid Method of 

 Virtual-Height Determination.^ J. P. Schafer and W. M. Goodall. 

 This paper describes a new method of determining the virtual height 

 of the ionized regions by visual observations of the received pulse 

 pattern on a cathode ray oscillograph tube, both for single frequencies 

 and for two frequencies simultaneously. A resume of the data ob- 

 tained during observations of some three hundred hours is given. 

 The frequencies used for these tests were 1604 kc, 2398 kc, 3256 kc, 

 4795 kc, and 6425 kc. A number of the tests included measurements 

 made upon two frequencies in rapid rotation. The more important 

 results may be summarized as follows: 



1. On a large number of occasions during the night, a phenomenon 

 has been observed apparently indicating an increase in the density of 

 ionization in the lower layer. This is important because the ionization 

 is usually assumed to decrease during the night hours. 



2. Reflections are often observed simultaneously from both ionized 

 layers. An explanation of this phenomenon is given. 



3. The virtual heights of the reflecting layers are rarely duplicated 

 from day to day for a given time and frequency. 



4. Large numbers of multiple reflections are frequently obtained 

 representing a path distance of over 5000 km. for the last reflection. 

 This fact indicates that the multiple-hop mode of propagation is 

 probable for long-distance transmission. 



The Principles of the Light Valve.^^ T. E. Shea, \V. Herriott, and 

 W. R. Goehner. The light valve has been used very widely as the 



^Rroc. I.R.E., July, 1932. 



10 Jour. S.M.P.E., June, 1932. 



