THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



— ♦ — 



[FOURTH SERIES.] 



JANUARY 1864. 



I. On the Adequacy of Laplace's Explanation to account for the 

 Discrepancy between the Computed and the Observed Velocity of 

 Sound in Air and Gases. By John Le Conte, M.D., Pro- 

 fessor of Natural Philosophy in the South Carolina College*. 



NOTWITHSTANDING the acknowledged incompleteness 

 and obscurity which characterizes his physical reasoning 

 on this subject, it is now universally admitted that the true 

 principles of the theory of the propagation of sound were first 

 enunciated (in 1687) by the immortal author of the Philosophise 

 Naturalis Principia. In the 43rd proposition of the second book 

 of the Principia, Newton shows how a body vibrating in an elas- 

 tic medium will propagate pulses through the medium. In the 

 47th proposition of the same book he attempts to investigate the 

 exact nature of the motion of the vibrating particles, and con- 

 cludes that the motion of each molecule necessarily follows the 

 law of the oscillating pendulum. In the 48th proposition he 

 establishes the fundamental principle in dynamics, that, in a 

 medium whose elastic force is proportional to the condensa- 

 tion, the velocities of pulses must vary directly as the square root 

 of the elastic force, and inversely as the square root of the density. 

 In the 49th proposition of the same book Newton deduces the 

 celebrated conclusion, that the absolute velocity with which such 

 pulses are propagated in the air is equal to that which heavy 

 bodies acquire by falling freely through half the height of a homo- 

 geneous atmosphere. And lastly, in the Scholium to the 50th 



* Communicated by the Author. Note. — This paper was completed and 

 ready for publication in July 1861 ; its transmission to England has been 

 Relayed by the interruption of communication incident to the great revolu- 

 tionary struggle in which we are engaged. 



Phil. Mag. S. 4. Vol. 27. No. 179. Jan. 1864. B 



