ABSTRACTS OF TECHNICAL PAPERS 371 



described. One consists of a regenerative vacuum-tube circuit, the 

 frequency of which is determined by the mechanical properties of a 

 tuning fork. The other is a regenerative circuit controlled by a 

 piezo-active crystal. Means are provided, in the case of each standard, 

 whereby the recurrent cycles may be counted by a mechanism having 

 the form of a clock, the rate of which is a measure of the frequency of 

 the reference standard. 



Data taken over a period of several years with a fork-controlled 

 circuit show that, under normal conditions, its rate may be relied upon 

 to two parts in one million. Data taken over a much shorter time 

 with crystal controlled oscillators indicate that they are about ten 

 times as stable. 



Plane Waves of Light. II. Reflection and Refraction.'^ Thornton 

 C. Fry. This paper extends the study of plane light waves, which 

 was begun in the Journal of the Optical Society for September, 1927, 

 to the phenomena of reflection and refraction. It develops the 

 general formulae for reflection from a plane boundary between two 

 media and for reflection from thin films, paying especial attention to 

 the situations under which "hybrid" polarization occurs. The dififer- 

 ences between the reflected and refracted components in the case of 

 dielectrics and metals are illustrated by a number of diagrams. 



The paper closes with a discussion of the determination of the 

 optical constants of metals, both from the state of polarization of the 

 reflected light and from the direction of emergence of the ray trans- 

 mitted through a prism. 



Propagation Characteristics of Sound Tubes and Acoustic Filter s.'^^ 

 W. P. Mason. This paper describes a method for making acoustic 

 propagation measurements, and presents the results of attenuation 

 and velocity measurements of straight tubes and acoustic filters. 

 The ordinary electrical transmission measuring circuit is employed in 

 conjunction with loud speakers and acoustic resistance terminations. 

 The process of measurement consists in obtaining the transmission 

 characteristics of the systems with the device to be measured in the 

 acoustic circuit, then obtaining the characteristics with the device to 

 be measured taken out of the acoustic circuit. The difference between 

 these two measurements gives the transmission characteristics of the 

 device to be measured between the two acoustic resistance termina- 

 tions. Results obtained from these measurements for straight pipes 

 agree well with the Helmholtz-Kirchoff Law. 



^ Journal of the Optical Society of America, Vol. 16, pp. 1-25, January, 1928. 

 '■''Physical Review, pp. 283-295, Vol. 31, No. 2, February, 1928. 



