ABSTRACTS OF TECHNICAL ARTICLES 177 



arithm of the viscosity. The increased power-transmitting capacity for 

 short pulse lengths is a result of the finite time taken for the small holes to 

 grow in size to a large enough hole to cause rupture of the liquid. 



Modulation in Communication.^ F. A. Cowan. The fundamentals in- 

 volved in introducing signals into one medium and transmitting them 

 through another are simplified in this review, so that the relationships be- 

 tween the many varieties of modulations attempted or in contemporary use 

 are formed into a cohesive whole. 



Air-borne Magnetometers J E. P. Felch,* W. J. Means,* T. Slonczew- 

 SKi,* L. G. Parratt, L. H. Rumbaugh and A. J. Tickner.* Developed 

 under the impetus of the submarine menace of World War II, the air-borne 

 magnetometer has found many peacetime uses. Navy airplanes equipped 

 with magnetometers for exploration of Antarctica were used in the recent 

 United States Navy expedition. An expedition now is studying the Aleutian 

 Alaskan volcanos and the Aleutian submarine trench. From there it will 

 proceed to Hawaii and Bikini. 



The Generation of Centimeter Waves} H. D. Hagstrum. The electronic 

 devices used most extensively, recently, for the generation of centimeter 

 waves are discussed. The physical form, operating capabilities, and the 

 basic physical principles of operation of the triode, velocity-variation, and 

 magnetron oscillators are presented. An attempt is made to show how these 

 oscillators are related to one another. For a variety of reasons, particular 

 emphasis is placed on the magnetron oscillator. 



Selective Demodulation} Donald B. Harris. A method of demodula- 

 tion is proposed in which the output current of the demodulator is a linear 

 function of the input voltage, while at the same time provision is made for 

 producing the necessary product terms which will result in demodulation. 

 Demodulation is brought about by integrating the product of the instan- 

 taneous value of the modulated wave by the instantaneous value of a wave 

 having the same frequency and phase as the carrier. Where this method of 

 demodulation is used it is proposed that two carriers in quadrature on the 

 same frequency may be employed, reducing the bandwidth to that re- 

 quired for single-sideband transmission. 



It is suggested that the required linear demodulation characteristics may 

 be obtained through the use of "electron-coupled" demodulators. Theo- 

 retical considerations indicate that, when demodulation of this type is em- 

 ployed, selectivity ahead of the demodulator may be dispensed with, the 



^Elec. Engg., September 1947. 

 7 Elec. Engg., July 1947. 

 * Of the Bell Sy Stan. 

 ^Proc. I. R.E., June 1947. 

 9 Proc. I. R. E., June 1947. 



