488 RECORDS 



dividing No. 2 gelatine capsules longitudinally so as to form half 

 cylinders and mounting them on card-board arms, the anemom- 

 eter rotated with ten revolutions per second in, the loop of the 

 wave and came nearly to rest in the node. The rate of revolu- 

 tion at various positions along the wave varied approximately 

 according to a sine curve. The maximum amplitude of the wave 

 as calculated from the above rate was 0.57 cm. 



The Kundt's figure experiment was performed by emptying a 

 box of No. 5 gelatine capsules into the middle of the loop. They 

 arranged themselves in rows across the pipe. Each capsule at- 

 tracted its neighbor at the ends and repelled it at the sides. The 

 experiment is quite striking. 



The motion of a cylinder perpendicularly to the stream lines 

 was obtained by using a capsule from which the cap had been 

 removed. Such a capsule moved in the direction of the closed 

 end with considerable force. This was also shown by making a 

 small mill with a capsule at the end of each of four card-board 

 arms. The rates of revolution in various parts of the wave made^ 

 when plotted, nearly a sine curve. The force acting normally 

 to the closed ends of the cylinders was measured with a torsion 

 balance. The square roots of the torsion deflection gave when 

 plotted an approximate sine curve. The experiment was per- 

 formed in air, illuminating gas, carbon dioxide, and hydrogen. 

 The torsion deflections were directly proportioned to the densities 

 of the gases. Prof. William Hallock first suggested the cause 

 of this effect, showing that it was due to the principle of Ber- 

 nouilli, that a gas in action is less dense than the same gas at 

 rest. The vibrating air has considerable velocity while the air 

 within the cylinders is nearly at rest. The force is due to the 

 difference of density on the two sides of the closed end of the 

 cylinder. The author used this principle to determine the am- 

 plitude of vibration. Prof. R. S. Woodward assisted him in 

 applying the proper hydrodynamical principles, and he calculated 

 that the change in density was such as to give a pressure of 2 i 

 dynes per square centimeter, while the amplitude was 0.33 cm. 

 This agrees closely with the value obtained with the sound wave 

 anemometer. 



