26 Prof. J. Le Conte on the Discrepancy between the Computed 



is a vera causa tending to augment the velocity of sound above 

 what it would be by the Newtonian formula. 



2. That the accuracy of the physical reasoning upon which 

 Laplace's formula is based has not been invalidated by the recent 

 discussions on the mathematical theory of sound. 



3. That, using the most recent and trustworthy experimental 

 data, Laplace's formula is fully adequate to bring up Newton's 

 velocity to the observed or measured velocity of sound. 



4. That, making use of the data furnished by the most accu- 

 rate thermo-dynamical experiments, the entire adequacy of 

 Laplace's explanation to account for the whole excess of the 

 observed velocity above that given by the formula of Newton 

 and Lagrange is confirmed in the most complete and satisfactory 

 manner. 



Before bringing this paper to a close, it may be proper to add 

 a few remarks in relation to the propagation of elastic pulses in 

 mixed gaseous media, such as the atmosphere. Three possible 

 cases present themselves: viz. {a) The vibrations of the particles 

 of the mixed gases may be regarded as giving rise to such inter- 

 ferences and anomalous collisions as to prevent the regular trans- 

 mission of pulses, and of course to interrupt the propagation of 

 sound, (b) The several gases may be considered as co-tenants 

 occupying the same space without interference, and consequently 

 each gas propagating its own elastic pulse independently of the 

 others with a velocity inversely proportional to the square root of 

 its density, (c) And lastly, between these two extreme cases 

 there is an intermediate one, in which a mutual action among the 

 particles of the constituent gases is contemplated. Let us con- 

 sider each of these cases separately. 



a. Under theirs/ head may perhaps be included the anoma- 

 lous results which Sir John Leslie observed in the case of a bell 

 sounded in a mixture of hydrogen and air. But as the atmo- 

 sphere obviously does not come under this case, I shall dismiss it. 



b. Some philosophers have thought that the aqueous vapour 

 of the atmosphere propagates sound quite independently of its 

 other gaseous constituents. The duplication of sound sometimes 

 observed in warm damp weather has been considered as probably 

 arising from a part of the sound being transmitted quicker than 

 the rest by the aqueous vapour*. If such is really the case, it 

 is rather singular that the phenomenon is not more frequently 

 recognized. It is desirable that more careful observations should 

 be made in relation to this point under circumstances precluding 

 the possibility of duplication from echoes. Moreover, the usual 



* Herschel's "Treatise on Sound/' in Encyc. Metrop. art. 109. Also 

 Herapath's ' Mathematical Physics/ vol. ii. p. 66. London, 1847. 



