ABSTRACTS OF TECHNICAL ARTICLES 179 



of short duration. Loudness tests were made on sounds persisting from 

 0.005 to 0.2 second and covering a wide range of levels. The observed in- 

 crease in magnitude of a sensation as the duration time is increased is 

 attributed to the integration characteristic of the central nervous system, 

 and an equivalent electrical circuit is derived. The circuit analogy is then 

 used in the computation of loudness as a function of the duration of the 

 stimulus. 



The Physics of Electronic Semiconductors.^^ G. L. Pearson. The band 

 theory of solids is capable of explaining such fundamental properties of elec- 

 tronic semiconductors as the dependency of specific resistance on impurity 

 content, the negative temperature coefficient of resistance, the sign of the 

 Hall and thermoelectric effects, and the direction of rectification. Measure- 

 ments of the specific resistance and the Hall constant enable the calculation 

 of density, mobility, and mean free path of the electric carriers as a function 

 of temperature and impurity. 



Automatic Frequency Control of Microwave Oscillators M Vincent C. 

 RiDEOUT. A method for the automatic frequency control of any type of 

 tunable microwave oscillator is described. In this method a servomechan- 

 ism is used which includes a wave-guide discriminator circuit, a mercury- 

 contact relay, a 60-cycle amplifier, and a small two-phase induction motor. 



Tests made on a preliminary model of a circuit of this type used with a 

 4000-megacycle oscillator showed that a stability of one part in 50,000 was 

 obtainable. The manner in which such a control system may be used in a 

 microwave repeater is described. 



Proposed Method of Rating Microphones and Loudspeakers for Systems 

 Use}^ Frank F. Romanow and Melville S. Hawley. Proposed, is a 

 method of rating microphones and loudspeakers whereby the over-all per- 

 formance of a sound system may be determined by adding together the 

 microphone and loudspeaker ratings and the gain of the interconnecting 

 network. This sum gives the performance quite accurately for most sys- 

 tems. However, in some combinations of elements correction terms must 

 be added. The formulas for these correction terms are derived. 



The proposed microphone and loudspeaker ratings have the additional 

 usefulness of being in a form which permits the comparison of instruments 

 of different impedances. 



Sulfur Linkage in Vulcanized Rubber}^ Milton L. Selker and A. R. 

 Kemp. The reaction of 2-methyl-2-butene with sulfur at 141. 6°C. was 

 studied. Reaction time and concentration paralleled those common in 



i3£/ec.£»gg., July 1947. 



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



15 Proc. I. R. E., Waves and Electrons Section, September 1947. 



i« Indus. & Engg. Chem., July 1947. 



