Velocity of Sound in Air. 333 



In the diagram (Plate VII.) the curve given by the figures 

 in Table VII. is laid down, and also the observed and calcu- 

 lated values given in Table VIII. To these are added curves 

 for 130, 520, and 1040 vibrations. 



In addition to the experiments of which the details are 

 given, many trials were made in the course of adjusting the 

 apparatus. Some of these trials were at pitches other than 

 those finally adopted ; and although such results were of no 

 value for exact comparison, the general bearing of them was 

 quite in agreement with the results tabulated. One of these 

 preliminary trials was a set of five observations with the tube 

 of 52-91 millim. diameter (r 3 ) at the pitch of 260. The mean 

 result was a velocity of 330*27, in place of 329*94 as on 

 Table VII. This trial was made with the tube before the 

 introduction of the bulb -mouth ; and the third partial tone 

 was perceptible to the ear, so that the prime may have been 

 influenced a little thereby. 



The notes were all purposely kept very weak, so that the 

 excess of pressure in the tubes when sounding, above the 

 barometric pressure, must have been very small indeed. In 

 one of the large tubes (r 3 ) a water-pressure gauge was intro- 

 duced ; but the pressure was barely measurable, certainly not 

 exceeding ^ inch of water. In the calculations I have there- 

 fore assumed that the influence of intensity might be neglected. 



The chief conclusions to which these experiments appear to 

 lead are the following: — 



1st. The tubes used for the measurement of wave-length, 

 as determined by the length between nodes, must speak with 

 a pure tone ; or 



2nd. If partials are present, the tubes must be of such 

 form as to have their proper tones in exact agreement with 

 the harmonic series. (Neither of these conditions is easily 

 attainable with ordinary organ-pipes.) 



3rd. The air-blast must not constrain the pipe to speak any 

 other pitch than its natural pitch of resonance. 



4th. In smooth tubes the diminution of velocity is propor- 

 tional to r~ ] and to n~i, as determined by Helmholtz. 



5th. The velocity V in free air for sound-waves of low 

 intensity, or just audible, is 331*676 metres at 0° C. 



6th. The ratio between the two specific heats of air, as 

 deduced from the Newtonian velocity 279*955 metres, and V 

 as above 331*676 metres, is 1*4036. 



As there is perhaps room for some doubt about the influence 

 of n being properly represented by n - *, I have not attempted 



