390 BELL SYSTEM TECIIMCA L JOl RXA L 



number of nodes on the treated walls. The "interaction effect" of one 

 strip on another is shown to decrease with an increase of the number of 

 nodes. The results are then applied to the case of ducts with non-uniform 

 distribution of absorbing material on its walls. Results are given which 

 permit the calculation of the attenuation per unit length of duct. The 

 methods of this paper hold for any distribution of absorbing material and 

 also if the admittance is a function of angle of incidence. 



High Current Electron Guns J' L. M. Field. This j)aper presents a 

 survey of some of the problems and methods which arise in dealing with 

 the design of high current and high current-density electron guns. A 

 discussion of the general limitations on all electron gun designs is followed 

 by discussion of single and multiple potential guns using electrostatic fields 

 only. A further discussion of guns using combined electrostatic and mag- 

 netic fields and their limitations, advantages, and some possible design 

 procedures follows. 



Reflection of Sound Signals in the Troposphere^' G. W. Gilman, H. B. 

 CoxHEAD, and F. H. Willis. Experiments directed toward the detection 

 of non-homogeneities in the first few hundred feet of the atmosphere were 

 carried out with a low power sonic "radar." The device has been named 

 the sodar. Trains of audiofrequency sound waves were launched vertically 

 upward from the ground, and echoes of sufficient magnitude to be displayed 

 on an oscilloscope were found. Strong displays tended to accompany 

 strong temperature inversions. During these periods, transmission on a 

 microwave radio path along which the sodar was located tended to be 

 disturbed by fading. In addition, relatively strong echoes were received 

 when the atmosphere was in a state of considerable turbulence. There was 

 a well-defined fine-weather diurnal characteristic. The strength of the 

 echoes was such as to lead to the conclusion that a more complicated distribu- 

 tion of boundaries than those measured by ordinary meteorological methods 

 is required in the physical picture of the lower troposphere. 



A Cathode-Ray Tube for Vieiving Continuous Patterns? J. B. Johnsox. 

 A cathode-ray tube is described in which the screen of persistent phosphor 

 is laid on a cylindrical portion of the glass. A stationary magnetic field 

 bends the electron beam on to the screen, while rotation of the tube produces 

 the time axis. When the beam is deflected and modulated, a continuous 

 pattern may be viewed on the screen. 



6 Rev. Mod. Pliys., July 1946. 



^ Jour. Acous. Soc. Amer., October 1946. 



''Jour. Applied Physics, November 1946. 



