Section III, 1922. [163] Trans. R.S.C. 



High Frequency Vibrations, and Elastic Modulus of Metal Bars 



By R. J. Lang, M .A. 



(Presented by R. W. Boyle, F.R.S.C. 



(Read May Meeting, 1922) 



A method which could be adopted to obtain the velocity of a 

 compressional wave and Young's elastic modulus of a metal bar is 

 that based on the device known as "Kundt's Tube." A rod of the 

 metal, a meter or so long, is clamped firmly at its central point, and 

 one end bears a light disc of thin metal which extends across with- 

 out touching a long glass tube. The opposite end of the tube is closed 

 by a similar disc, the position of which is adjustable, and in the 

 bottom of the tube a very little powder of lycopodium seed is 

 scattered from end to end. If the end of the steel rod remote from 

 the glaiss tube be now stroked with a piece of chamois skin covered 

 with powdered resin a note of high frequency will be emitted by the 

 rod, and, if the adjustable disc be properly placed, standing waves 

 are formed in the air in the glass tube, the nodes and loops of which 

 register in the dust in the tube. A very simple calculation is all that 

 is necessary to obtain the velocity of the wave in the metal rod and 

 Young's modulus for the rod. 



The purpose of this paper is to describe an even simpler method 

 for arriving at the same results, which appears to the author to 

 have certain advantages over the method devised by Kundt. For 

 example a steel bar, 2.54 cms. in diameter and 30 cms. long, was 

 firmly clamped at its middle point by a special, tempered, steel 

 clamp, in which the actual surface bearing upon the bar was only 

 about 2 mm wide and fitted into a shallow groove cut around the 

 bar at this point. This clamp made it possible to fix the steel bar 

 rigidly to a stone table. (See diagram.) Opposite one end of the 



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