Stress and Strain on the Properties of Matter. 



93 



The Longitudinal Elasticity as determined by the Method of Longitudinal 



Vibrations. 



Preliminary Trials. 



As it; was found necessary to nse the syren more or less throughout 

 this part of the investigation, some experiments were made with a 

 view of ascertaining how far this instrument could be relied on for 

 determining the number of vibrations made in a given time. First, 

 attention was directed to the registering apparatus, with the object of 

 determining how far the putting of this in, or the taking of it out of 

 action, would introduce error. Any error of the kind would be more 

 manifest when the number of vibrations was determined for a short 

 space of time than for a long one, and in the following experiment it 

 will be seen that there is no appreciable error due to the inertia of the 

 register. 



Experiment IV. 



The number of vibrations recorded in one minute by the syren in 

 each of three trials, when the syren was kept in unison with a mono- 

 chord, were : — 



Number of trial. 



Number of vibrations. 



1 



813 x 20 



2 



812 x 20 



3 



811 x 20 





812x20 



The number of vibrations recorded in five minutes was next ascer- 

 tained by one trial to be 4064 x 20, which would give 812*8 X 20 per 

 minute, or only 0*1 per cent, higher than before. The pitch of the 

 monochord was then altered, and several fresh experiments similar to 

 the above ended in showing that sometimes the number of vibrations 

 per minute registered in the shorter-timed trials appeared to be 

 greater, and sometimes less, than the number registered in the longer- 

 timed trials, the difference being in all cases equally slight with the 

 above. 



Again, the syren was employed to determine the pitch of several of 

 Koenig's forks ; thus in a single trial, in each case of three minutes' 

 duration, the instrument registered 256*7 and 513*8 vibrations per 

 second respectively for two forks, which were marked with the num- 

 bers 256 and 512. Several other trials of similar accuracy, sometimes 

 giving slightly greater, and sometimes slightly less vibration- frc- 



