172 BULLETIN OP THE 



It would follow from this experiment that the echo is not a 

 reflection from a definite surface, since it would then increase in 

 loudness as the surface is approached ; but a series of rebounds 

 from points at various distances. 



Another fact of great importance in determining the nature of 

 the echo is that derived from the observations of the keeper at 

 Block Island ; he has recorded during the observations of a yeai*, 

 every Monday, the length of the continuance of the echo, the 

 state of the weather, the direction of the wind, and the other 

 meteorological data. Prom which it is found that the echo is 

 always heard with the sound of the syren during a wind in any 

 direction, and of all intensities ; but with less duration after the 

 original blast, during the oecurrence of a very high wind, than in 

 calmer weather ; and, above all, that it is heard equally well 

 during a dense fog, when evidently the air must be homogeneous 

 and saturated in every part with vapor. 



From these facts it appears to me conclusive that the reverbe- 

 ration, constituting the ocean echo, cannot be due to invisible 

 clouds. The only hypothesis which suggests itself to my mind 

 as a basis of further investigating this subject, is that in the 

 spread or divergency of the sound the direction of the impulse 

 turns through an angle of a little more than 90°, so as to meet 

 the surface even of the smooth ocean in a direction by which it 

 would be reflected to the ear of the observer, making the angle 

 of reflection equal to tjae angle of incidence; although from the 

 gradual dispersion of sound-beams, the precise equality of these 

 angles is obviously not very important to the result. 



On returning from this excursion by the N. Y. Western Rail- 

 way to the Hudson River at Troy, opportunity was taken to make 

 some observations on the action of sound in the Hoosac tunnel, 

 through which I passed, accompanied by Mr. E. L. Woodruff, 

 on the afternoon of September lih. Resting at East Windsor 

 near the western outlet, I spent a considerable part of the follow- 

 ing day in making an examination of the work. Mr. W. P, 

 Granger, the chief engineer, and Mr. A. W. Locke, his principal 

 assistant, very courteously furnished a hand-car, and cordially 

 proffered every facility for making any desired investigations. 

 This tunnel, as is familiar to most of those present, is nearly 

 five miles long, rising by an easy grade of 26.4 feet to the mile 

 from either mouth to about the middle of the tunnel, where it 



