Page:Aerial Flight - Volume 1 - Aerodynamics - Frederick Lanchester - 1906.djvu/438

App. II. D. It would appear from the above transcript that Poynting unquestionably held the view on June 7th, 1905, that a Boyle's law wave train would give rise to pressure increase or momentum transference, just as he held this view at the time of his address to the Physical Society in February of that year. Furthermore, it is evident that, at the time in question, result (2) was not a consequence anticipated by Poynting, for in another communication about the same date in reply to the author he says:—"I have not thought of the sound pressure as accounted for by the kinetic theory of gas. S. Tolver Preston, I think, did so somewhere. It appears to me best in the first place to get at the idea as I have done in the paper as resulting from known observable properties. Then go to the kinetic theory if you like.

The perfectly elastic solid—if by that is meant one that obeys Hook's law rigidly—would give pressure apparently from Larmor's theorem."

It is difficult to understand how Prof. Poynting can have been led to make so extraordinary a statement as that contained in his present letter in view of the facts above given, and the author trusts that he will see his way to give publicity to some adequate explanation.