B. Dams — Small closed Cylinders in Organ-pipes. 189 



position of the node of the next overtone. When this over- 

 tone occurred, the rows would divide into two portions, 

 which moved toward the middles of the two loops of the 

 new stationary wave. 



A striking effect was obtained by placing a number of the 

 smallest capsule-cylinders a short distance from the node. 

 When the pipe spoke, they immediately ran rapidly to the 

 middle of the loop, and there assumed a regular arrangement. 



The effects described in this paper are of course of the same 

 nature as the Kundt dust figures. The individual capsule- 

 cylinders may be considered as dust particles in which the 

 size has been much increased, the particles still remaining 

 light enough to respond readily to the delicate forces to which 

 they are subjected. 



Prof. Rood suggested as an explanation of the spacing that 

 a sound-shadow is formed on the two sides of the cylinders at 

 each half vibration, alternately. These shadows, being regions 

 of less motion, press so to speak against the cylinders. When 

 there are two rows the shadows between the cylinders press 

 them apart until the force just equals that pressing against the 

 outside or nodal sides of the two cylinders. This also explains 

 their rapid movement from the nodes toward the loop. The 

 average velocity on the side nearest a node is less, and hence 

 the pressure greater than on the side nearest a loop, where the 

 velocity is greater. The behavior of the capsule-cylinders 

 illustrates the distribution of the forces acting upon rigid bodies 

 in moving fluids, the mathematical analysis of which has been 

 so fully developed by W. Koenig.** 



The effect here described can be easily reproduced as a lec- 

 ture experiment. The ordinary stopped organ-pipe found in 

 lecture cabinets will suffice for the purpose. The smaller cap- 

 sules will perhaps be found to give the effect more strongly in 

 case the pipe is not a powerful one. 



Physical Laboratory of Columbia University, June 1, 1901. 

 * Wied. Ann., xlii, pp. 353, 549, 1891. 



