£96 Mr. R. IT. M. Bosanquct on the Present 



the old toothed-wheel apparatus, and the flashing machine of 

 Lord Rayieigh are examples of instruments which will acquire 

 a new importance for this purpose when driven hy a uniform 

 motor. 



Revolving Stopcock. 



There is a large class of investigations which depend on the 

 regular opening and closing of a channel, for the interruption 

 either of a current of wind or of a current of sound. A turn- 

 table fitted with revolving stopcocks has been constructed for 

 these investigations; and rough results are obtained without 

 difficulty ; but it is only by the employment of the uniform 

 motor that accurate results can be expected. 



The dissipation of sound in resonators and organ-pipes is a 

 problem which may be attacked by means of the interrupted 

 current of wind. What is the length of a periodic interrup- 

 tion in the wind-supply of a pipe or resonator which just fails 

 to break the continuity of the tone ? The answer to this ques- 

 tion, and the phenomena we come across in the process of ob- 

 taining it, furnish important contributions towards our know- 

 ledge of aerial mechanics. 



Another problem depending on interrupted wind-supply is, 

 the determination of the velocity of sound in the open air for 

 different musical notes, by a process bearing some slight ana- 

 logy to Fizeau's determination of the velocity of light by re- 

 flection from a distance. The corridor of a cloister supplies 

 an excellent locale. The sound is emitted by the apparatus at 

 such intervals that a number of echoes (4, 6, or 8) are heard 

 between two successive sounds. The mode of calculation is 

 obvious. 



A problem depending on the interrupted current of sound 

 is, If the ear listen to a sound through the interrupted channel, 

 what are the phenomena presented ? They are of some com- 

 plexity and considerable interest. Professor Mayer has pub- 

 lished experiments on the subject. 



Reeds. 



Notwithstanding the investigations that exist on the beha- 

 viour of reeds with respect to columns of air with which they 

 are connected, the subject is still involved in considerable ob- 

 scurity. There are different kinds of reeds, which possess very 

 ■ different properties; and there is ample room for a thorough 

 experimental investigation. With the appliances of the pro- 

 posed laboratory these investigations are within reach. 



The revolving stopcock can be used to admit wind to the 

 bottom of a pipe or resonator, and so separate out those effects 

 which may be regarded as the results of inexorable motions of 



