Mr. R. H. M. Bosanquet on the Theory of Sound. 273 



throw a light on the subject which appears to have been in- 

 sufficiently appreciated. 



In the next place, his proceedings bring to light the diffi- 

 culty in correctly allowing for wind &c. He always employed 

 reciprocal discharges in the open-air experiments ; but it was 

 clear that accidental influences were not entirely eliminated. 

 This consideration alone furnishes an objection fatal to the 

 authority of all experiments not conducted hj reciprocal dis- 

 charges. 



There is also a question as to the direction of transmission 

 not being rectilinear in the neigbourhood of the gun, the error 

 arising from which Regnault's arrangements eliminated. 



The memoir occupies the earlier half of the volume of me- 

 moirs of the Institute for 1868 ; I cannot undertake to repro- 

 duce even a sketch of the results, more especially as a short 

 summary by Regnault himself was printed at the end of the 

 former edition of Tyndall on Sound. 



The result of the study of propagation in tubes above alluded 

 to is, that the disturbances arising from the class of sounds 

 employed (pistol-shots ) had for some distance from their origin 

 a velocity comparable with the value ordinarily received for 

 the velocity of sound, that as the disturbance diminished its 

 velocity grew less ; and the last velocity registered by the 

 apparatus in tubes, even 1 metre or more in diameter, was 

 always less than the value 330*7, which he announces as his 

 mean result for the open air. 



The mean results always denote the mean velocity from 

 end to end of the course. There is much that is difficult 

 in the reception of these mean velocities, which are really 

 fictitious quantities, for any theoretical purpose. But the 

 mere recognition of their nature, and the approximate distinc- 

 tion drawn between them and the true velocities at different 

 parts of the course, constitute really a greater advance in the 

 subject on the part of Regnault than any thing that we have 

 received from other experimenters. The influence of the dia- 

 meters of the tubes containing the gases, too, is an element of 

 the utmost importance. For instance, in the Table just given 

 there is a determination by Le Roux* which appears to coin- 

 cide closely with Regnault's ; but on consideration it is seen 

 that in all probability two different elements enter into the de- 

 termination, either of which would alone produce a devia- 

 tion, and an accidental compensation occurs. The disturb- 

 ance is taken in the earlier stage, when, according to Regnault, 

 the velocity would be considerably greater ; and it is propa- 



* Ann. de Chim. et de Phys. 4 e ser. toL xii. p. 345. 



Phil Mag. S. 5. Vol. 3. No. 18. April 1877. T 



