58
THE ERUPTION OF PELÉE
in sound-carriage. I t would appear t h a t on the evening of Aug. 30, when Morne Rouge was destroyed, the reports of explosions were distinctly heard on the island of St. K i t t s some time in advance of the main cataclysm, or as reported at 8.07 and 8.25 P.M. (Monthly Weather Review, October, 1902, p. 487). The peculiarity of the explosions being heard with terrific intensity at remote points and hardly, if at all, near by, was also exhibited in t h e K r a k a t a o erup tion, t h e report from which was carried to the island of Rodriguez, three thousand miles away—the farthest distance from a point of origin at which sound has ever been heard, or a t least recorded (Royal Society Report). General Strachey (p. 79) believes t h a t " p r o b a b l y this peculiar phenome non was caused b y the large a m o u n t of solid m a t t e r " which a t the time of the eruptions " w a s ejected into the atmosphere b y the volcano, and which formed in the lower s t r a t a of the air a screen of sufficient density to prevent the sound-waves from penetrating to those places over which it was more immediately suspended." This explanation, so contrary to the results t h a t have been obtained b y Tyndall and others in their experiments upon the transparency and opacity of the atmosphere in relation to the passage of sound-waves—the unexpected determination t h a t the dissemination of solid particles in the air, the presence of fog, rain or snow, etc., has little or no effect upon the transmission of sound—it seems to m e can hardly be the correct one; nor, indeed, can it find application to the conditions which existed a t the time of the eruption of August 30, when I was located at the Habi tation Leyritz. We were then practically under, and not behind, the volcanic cloud, through which came quite distinctly the muffled, b u t continuous, roar of the volcano. If the obscuration of sound b y solid particles was really produced, the phenomenon m u s t have taken place within the body or v e n t of the volcano itself. I should rather believe t h a t the acoustic interruption was in some way associated with an atmospheric disintegration—the presence within the atmos phere of layers of differing thermal power and differing vaporous constitution producing, to use Tyndall's words, acoustic clouds t h a t are "flocculent to sound" ("Lectures on Sound," 1875, p. 321).* This would, however, still leave unexplained the transmission of the sound to great distances, unless, indeed, we m a y be permitted to assume t h a t the propagation of the sound waves has been carried to distant points through the materials of the solid crust. Can it be thought t h a t the sounds coming as if thrown down b y the clouds, noted b y Mr. Plumacher at Maracaibo and by others in the island of Trinidad, were reflections from lofty "acoustic clouds," to which the sound waves were transmitted through the central orifice of the volcano? This suggestion is thrown out with m u c h diffidence, and only because no ordinarily * The remarkable experiments made by the distinguished British physicist in connection with the Trinity House have established the existence of conditions of absolute opacity to sound in an atmosphere that is optically transparent and shown the fallacy of the still commonly accepted notion that a direct relation exists between a clear atmosphere and the transmission of sound.