518 RESEARCHES IN SOUND. 



character to those which had been observed on the preceding day, and 

 the earher part of the same day, was prodnced. 



August 10. — Barometer 30.10 inches. Dry bulb 74° ; wet bulb G9^ F. 

 Wind W. S. W. ; atmosphere hazy. Observations first made with the 

 trumpet horizontal. Echo as that of preceding days, distinct but not 

 very loud, and coming principally from the portion of the horizon in the 

 direction of the axis of the trumpet. The position of the trumpet was 

 then changed, its axis being turned to the zenith in order to make what 

 was thought might be a crucial experiment. When the trumpet was 

 now sounded a much louder echo was produced than that which was 

 heard with the axis of the trumpet horizontal, and it appeared to encircle 

 the whole horizon ; but though special attention was directed to the point 

 by all the party present, no reverberation was heard from the zenith. 

 The echo appeared however to be more regular and prolonged from the 

 ocean portion of the horizon than from that of the land. 



In this experiment, while there was no reflection from the zenith in 

 which the sonorous impulse was strongest, there must have been 

 reverberations from the surfiice of the land and the ocean. This will 

 be evident when we consider the great divergency of sound by which 

 sonorous waves from a vertical trumpet are thrown down to the 

 plane of the horizon on every side, some of which, meeting oblique sur- 

 faces, must be reflected back to the ear of the observ^er near the source 

 of the sound. This inference will be more evident when it is recol- 

 lected that the reflected rays of sound diverge as well as those of the 

 original impulse. Hence reflection from the surface of the sea is a true 

 cause of the echo, but whether it be a sufficient one may require fui'ther 

 investigation. For this explanation it is not necessary that the sea 

 should be covered with crested waves ; a similar effect would take place 

 were the surface perfectly smooth but in the form of wide swells, which 

 in places exi)osed to an open sea are scarcely ever absent. Moreover, 

 the increased loudness of the echo is a fact in accordance with the same 

 view. 



The observations were repeated with the same effect on succeeding 

 days, until this class of experimenlfs was ended by the bursting of the 

 India-rubber tube. Had a distinct echo been heard from the zenith, the 

 result would have been decidedly in favor of the hypothesis of a reflec- 

 tion from the air ; but as this was not the case the question still remained 

 undetermined, especially since the atmosphere during these experiments 

 was evidently in a homogeneous condition. We do not agree however 

 in the position taken in the report of the Trinity Board, that on the 

 origin of this echo depends the whole solution of the problem as to the 

 efficient cause of the abnormal phenomena of sound. The ingenious ex- 

 perimental illustrations of the reflection of sound from a flame or heated 

 air, establish clearly the ijossibility of such reflection ; but it must be 

 remembered they were made under exaggerated conditions, the atmos- 

 X)here being in a state of extreme rarefaction in a limited space, and the 



