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



experimentalists till it is now large enough really to justify the 

 opinion which has been expressed, that to Laplace is due the 

 honour of having completed the solution, which was begun in 

 England, of the problem of the propagation of sound. And, to 

 speak candidly, it must be confessed that Laplace's sagacious 

 suggestion undoubtedly has the air of a vera causa, although it 

 requires a larger development of heat by the sound-wave than 

 seems probable. But its great defect, if I may be allowed to 

 consider it defective, is that the result it gives does not come up 

 to experiment. The theoretical velocity, after being amended 

 by Laplace's suggestion, still falls short of the experimental 

 velocity by 24 feet, if we take this last to be 1090 feet ; and by 

 76 feet if we take the velocity of sound to be 1142 feet as de- 

 termined by Derham, Flamsteed, Halley, and the Florentine 

 Academicians. It should be remembered also that theory 

 might a priori be expected to give a result exceeding, rather 

 than falling short of, experiment ; for theory assumes the elas- 

 ticity and fluidity of the atmosphere to be perfect, and we have 

 reason to think both are really in a slight degree imperfect; and 

 this is not likely to accelerate, but rather to retard (if it at all 

 affect) the propagation of sound-waves. Upon the whole, after 

 considering the matter in as impartial a spirit as possible, candour 

 obliges me to confess that Laplace's suggestion does not furnish 

 a sufficient cause. I do not deny that it may be a cause ; but it 

 is not the whole. There is a cause, still unrevealed, for the de- 

 fect of the theoretical velocity " *. 



The views advanced in the foregoing extract demand notice in 

 relation to several points. 1. That the value of the coefficient k 

 should have augmented with the increasing refinements of methods 

 of experimentation, is precisely what might have been a priori 

 expected ; for it is obvious that all the errors arising from im- 

 perfections of methods and instruments tend to depress its value 

 below its true amount. It is therefore hardly admissible to 

 ascribe this fact to any bias on the part of the experimentalists. 

 2. The charge that the experimental velocity of sound under- 

 went a " sudden and startling " diminution after the announce- 

 ment of Laplace's suggestion, is not supported by historical facts. 

 It is generally admitted by physicists, that the only reliable 

 determinations of the velocity of sound made anterior to 1816, 

 were those of the French Academicians in 1738, and of Benzen- 

 berg in 1809. The results in both of these cases, when reduced 

 to the standard temperature, do not differ sensibly from the later 

 determinations of the French and Dutch experimentalists. 3. 

 How little the theory in question is amenable to the objection 

 i( that the result it gives does not come up to experiment," will 

 * Phil. Mag. S. 4. vol. xix. p. 450 (1860). 



