114 BULLETIN OF THE 



sudden shutting down of the lid of a tool-chest. The unequal 

 or somewhat intermittent character of the echo appeared to result 

 from the irregular surface of the rock forming the walls of the 

 tube. A somewhat similar echo is sometimes returned from the 

 dense foliage of trees. It is proper to add that a very percep- 

 tible echo was heard from the portion of the tunnel lined with 

 brick. The efiPect could in neither case be ascribed to any invis- 

 ible " flocculence," as the air must have been in a very homogene- 

 ous condition. 



Inasmuch as in such observations the waves of sound are 

 reflected back to the ear from points at a considerable distance 

 from their origin, this being especially true of the ocean-echoes, 

 we are liable to be seriously misled if we rely too confidently on 

 the experiments of the laboratory ; and form hasty generalizations 

 from apparent analogies, without carefully considering all the 

 meteorological conditions by which the rays of sound may be 

 deflected, distorted, and diverged. It is now well established by 

 numerous observations and experiments — made independently on 

 both sides of the Atlantic, that the lines of acoustic propagation 

 (^conveniently called sonnd-beams) which are sensibly very recti- 

 linear for the distance of a hundred or two hundred feet, and 

 which are thus obedient to the katoptric and dioptric laws of 

 precise focal convergence, by means of solid mirrors and of gas- 

 eous lenseSj are yet at the distance of a few miles so strangely 

 contorted and aberrant, as seemingly to contradict all the analo- 

 gies suggested by our experience with the rays of light. It is 

 the accumulation of comparatively slight divergencies continued 

 through many thousands of yards, whether under the influence 

 of constant conditions, or of changing and reversed conditions, 

 which produces such marked anomalies at the distance of five or 

 of ten miles, and which makes their investigation as laborious as 

 it is instructive and important. And not until we have mastered 

 all the conditions affecting the transmission of sound throughout 

 its entire sensible range, and have thus become enabled to pre- 

 dict its true course, and to announce its varying limits of audi- 

 bility at the earth's surface, under given circumstances, can we 

 be said to have perfected the theory of this most interesting and 

 indispensable agent of communication. 



Remarks were made by Mr. Antisell. 



