ABSTRACTS OF TECHNICAL ARTICLES 687 



sound recording and photography in such a manner that a pleasing 

 illusion of reality is created in the theater. 



A Device for the Precise Measurement of High Frequencies.^ F. A. 

 POLKINGHORN and A. A. RoETKEN. A description is given of equip- 

 ment which has been constructed for the measurement of radio fre- 

 quencies between 5000 and 30,000 kc. The equipment consists of a 

 million-cycle quartz-crystal oscillator as a standard of frequency, 

 means for producing harmonics and subharmonics of this frequency, 

 and means for combining voltages of these known frequencies with a 

 voltage whose frequency it is desired to measure so as to produce beat 

 frequencies in successive stages, the beat frequency produced in each 

 stage having one less digit than that in the preceding stage. A cali- 

 brated electric oscillator is used to measure the frequency of the last 

 stage. An indicator gives the frequency of the unknown after a series 

 of dial adjustments. The precision of a completed measurement is 

 estimated at better than three parts in a million. 



Radio Transmission Studies of the Upper Atmosphere.'' J. P. 

 ScHAFER and W. M. Goodall. In this paper are given a number of 

 measurements which show time variations in the virtual height of the 

 ionized regions of the upper atmosphere. These measurements were 

 usually made simultaneously on two frequencies, 1604 kc. and 3088 kc. 

 Single frequency data are also given. The following are the main 

 points of interest presented. 



(1) The data indicate the existence of two distinct ionized regions or 

 layers. The changes in virtual height are sometimes very abrupt. 

 The existence of the lower layer even at night is indicated by an oc- 

 casional return to low virtual heights during this period. 



(2) Experimental evidence has been found of large retardations in 

 group velocity near the critical conditions for which the waves just 

 penetrate the layer to the point of maximum ionization. (Fig. 1) 

 Absorption is especially marked at such times. 



(3) Except at these critical periods the records for the simultaneous 

 transmissions show that the virtual heights of the upper layer are 

 greater for the higher frequency than they are for the lower frequency. 

 This statement would probably hold for the lower layer but no evidence 

 on this point is presented. 



(4) In the discussion several possible methods of two-layer formation 



are suggested, one of which involves the formation of negative ions in 



the region between the layers. 



^Proc. I. R. £., June, 1931. 

 'Prac. I. R. E., August, 1931. 



