134 Scientific Proceedings, Royal Dublin Society. 



at points nearer to the reed than where the rise had taken place 

 on going outwards. This is represented by the dotted part. The 

 diagram for a lower reed would consist of only short portions of 

 the higher parts of the curve, the reed only sounding at the corre- 

 sponding positions of the piston in the tube. 



On putting cork dust into the side tube, Kundt's figures formed 

 themselves, and made it plainly visible to the eye what was occur- 

 ring as the piston was pulled out. The dust was seen to keep 

 collected in a heap behind the piston until the pitch of the reed 

 rose for the second time, when, of course, there were two heaps 

 formed, and so on as the piston was withdrawn. At first, when 

 the lower note was sounding, evidently the half wave was situated 

 partly in the control tube and partly in the supply tube, the reed 

 being between the loop in the supply tube and the node in the 

 control tube. When sounding freely the reed was practically at a 

 loop, and remained so as the piston was drawn out, the distance to 

 the first node in the control tube varying. 



One of the advantages in using resonating side tubes, in study- 

 ing vibrations in tubes carrying air currents, is, that Kundt's figures 

 ean be employed to show to the eye what is going on, the dust not 

 being blown away, as it would be if put into the main tube. 



Experiments were next made as to how the length of the 

 supply tube affected the reed. The reed was fixed to the eud of 

 a glass tube, and this in turn to a narrower rubber tube. It was 

 found that there was always a tendency for a node to form at this 

 point. When the glass tube was a quarter of a wave length long, 

 or shorter, the reed sounded freely, but if longer, the pitch of the 

 reed was diminished, or ceased altogether ; but when a tube of 

 three-quarters of a wave length was used, the reed vibrated freely 

 again, and so on. 



From all these experiments it would appear that a reed vibrates 

 most freely near a loop ; but the fact that Helmholtz, 1 in his theory 

 of reeds, deduced that they ought to be found at a node, made it of 

 importance that a more careful examination of the oase should be 

 made. So to further test the position of the reed with respect to 

 the nearest node when sounding freely, the control tube was in- 

 serted at right angles as before in the supply pipe, but at a dis- 



1 Jamin, Cours de Physique, tome iii., fas. i., p. 56. 



