530 RESEARCHES IN SOUND. 



OBSERVATIONS ON THE ECHO AT LITTLE GULL ISLAND. 



The first observations to be mentioned are those relating to the echo ; 

 the results, however, in regard to this are not very satisfactory. The 

 sirens were of the second order, and therefore the echoes produced were 

 not as distinct as those from the larger instrument at Block Island. 

 The echo from the horizontal trumpet was distinct, and in the prolonga- 

 tion of its axis ; the interval however between the blast of the siren 

 trumpet and the commencement of the echo was very brief; so short, 

 indeed, that the ending of the one and the beginning of the other were 

 generally difficult to distinguish. A sligh't leak in the ai)i)aratus of the 

 siren produced a continuous hum, which interfered somewhat with the 

 distinct appreciation of the sound of the echo. The keeper thought the 

 weather was not favorable for the production of echoes. He thinks 

 they are heard most distinctly during a perfect calm, which did not occur 

 during the course of these investigations. 



The axis of the siren with the movable trumpet being directed to the 

 zenith, strict attention was given by all the observers to any echo which 

 might be produced from it; but in this case, as in that at Block Island, 

 the slight echo which was heard came from all points of the horizon. 

 On one occasion General Woodruff called attention to a small cloud pass- 

 ing directly over the zenith, from which a few drops of rain fell upon the 

 platform on which the light-house is erected. Advantage was taken of 

 this occurrence to direct strong blasts of the siren toward the cloud, 

 but no perceptible echo was returned. We have failed, therefore, in 

 this series of investigations, to obtain any positive facts in addition to 

 those already known as to the character of the echo. In regard to the 

 hypothesis offered for its explanation, if we found little in its supi)ort, 

 we have met with nothing to invalidate it. But whatever may be the 

 cause of the phenomenon, we do not consider it an imjiortant factor in 

 explanation of the results we have obtained, since it was too feeble to 

 produce any effect in the way of absorbing any notable part of the 

 original sound. Its importance from Dr. Tyndall's point of view is its 

 apparent support of the hypothesis of a flocculeut condition of the 

 atmosphere. 



OBSERVATIONS ON EFFECT OF ELEVATION ON AUDIBILITY. 



The next class of experiments at Little Gull Island had relation to 

 the effect of elevation on sound. The conditions here, however, for ar- 

 riving at definite results on this point were by no means as fovorable as 

 those at Block Island. The height which could be commanded was only 

 that of the tower of the light house, the gallery of which is 74 feet 

 above the i^latform upon which the buildings are erected, and 92 feet 

 above the level of the sea, much less than that at Block Island. Be- 

 sides this, the variableness of the wind at the surface of the ocean and 

 at heights above was not favorable for the illustration of the point in 

 question. 



