ABSTRACTS OF TECHNICAL ARTICLES 771 



the base edge face contacting the liquid). The two beams traverse the prism 

 to the base, where they are refracted into the test liquid as confluent beams. 



In Cases A and B, simulated interference (by optical integration), and 

 in Case C true interference, each give a light and dark band interference 

 pattern on the screen, whose band spacing is used in calculating the velocity 

 of sound in the test solid. The other required factors are the optical image 

 magnification, the frequency of the sound, the angular disposition of the 

 one or more acoustic surfaces of the test solid relative to the incident sound 

 beams, and in Cases A and B the velocity of sound in the reference medium. 

 Other variations of arrangement are suggested. 



Advantages of the improved methods are simple preparation of test speci- 

 men, directness and simplicity of measurement and calculation, good ac- 

 curacy, low sonic power requirements. A table of measured velocities (and 

 attenuations) in two metals and in numerous plastics and polymers show 

 the wide range of materials that may be measured by the new interference 

 methods. 



Ferromagnetic Resonance in Various Ferrites. W. E. Yager\ F. R. 

 Merritt\ and C. Guillaud^ Letter to the editor. Phys. Rev., v. 81, pp. 

 477-478, Feb. 1, 1951. 



The Study of Size and Shape by Means of Stereoscopic Electron 

 Micrography * C. J. Calbick^ Photo grammetric Engineering, v. 16, pp. 

 695-711, Dec, 1950. 



Electrical Excitation of Nerves in the Skin at Audiofrequencies * A. B. 

 Anderson^ and W. A. Munson^ References. Acoustical Soc. Am., JL, v. 

 23, pp. 155-159, Mar., 1951. 



Abstract — ^This is a report of results obtained in preliminary tests of 

 perception of signals applied directly to the skin in the form of electrical po- 

 tentials. The lowest signal level that could be felt and the highest level that 

 could be applied without extreme discomfort to the observers were deter- 

 mined for sine wave potentials ranging from 100 to 10,000 cps. The differ- 

 ence between the lowest and highest levels was about 25 db over 

 this frequency range. 



Difference limen measurements for intensity and frequency showed that 

 intensity discrimination is not greatly different from what it is for hearing 

 but the ear is vastly superior in the matter of frequency discrimination. 



Field Variation of Superconducting Penetration Depth. J. Bardeen^ Letter 

 to the editor. References. Phys. Rev., v. 81, pp. 1070-1071, Mar. 15, 1951. 



Determination of the Efects of Dissipation in the Cochlear Partition by 



* A reprint of this article may be obtained on request. 

 1 B. T. L. 



