On the Velocity of the Sound of Thunder. 37 



gases, and deduced from experiments a value of the mean length 

 of path of a particle between successive collisions. 



We have applied the theory to the law of diffusion of gases, 

 and, from an experiment on olefiant gas, we have deduced a 

 value of the length of path not very different from that deduced 

 from experiments on friction. 



Using this value of the length of path between collisions, we 

 found that the resistance of air to the conduction of heat is 

 10,000,000 that of copper, a result in accordance with experience. 



Finally, by establishing a necessary relation between the mo- 

 tions of translation and rotation of all particles not spherical, we 

 proved that a system of such particles could not possibly satisfy 

 the known relation between the two specific heats of all gases. 



III. On a New Theoretical Determination of the Velocity of 

 Sound. By the Rev. S. Earnshaw, M.A., Sheffield. 

 [Continued from vol. xix. p. 455.] 

 On the Velocity of the Sound of Thunder. 



I INHERE yet remains to be considered a case of sound-velocity 

 A to which the investigations of Newton and the suggestion 

 of Laplace are totally inadequate, which nevertheless is naturally 

 suggested, by what has been done in the preceding articles, as 

 necessary to complete the theory of sound-velocity : I allude to 

 the propagation of the sound of a clap of thunder. The con- 

 sideration of this case will strengthen the evidence of the sound- 

 ness of the preceding investigations. 



Before it was announced by myself at the Meeting of the 

 British Association at Leeds in 1858, that according to theory 

 violent sounds are propagated more rapidly than gentle sounds, 

 I believe the fact was not suspected by philosophers. I was led 

 to this result by a careful discussion of the integral of the 

 well-known equation of motion of an elastic fluid in a horizontal 

 tube. I was, however, not able to bring forward any instance 

 of the fact having been observed, except a single one, recorded 

 in one of Parry's Voyages to the North. The records of 

 experimentalists agreed in stating, on the contrary, that all sounds 

 travel at the same rate. Since that time the subject has rested. 

 A few weeks ago, however, my attention was recalled to it by the 

 receipt of a memoir printed in the Bulletins de VAcademie Royale 

 de Belgique, kindly forwarded to me by its author, Professor 

 Ch. Montigny of Antwerp, which has satisfied me that, in the 

 case of a thunder-clap, sound is sometimes propagated with a 

 velocity far greater than I had ever imagined, and that the 

 problem of the propagation of sound is yet far from having been 

 fully solved. 



