RESEARCHES IN SOUND. 503 



eugineer of tlie tliird district. We proceeded on this occasion in the 

 steamer Mistletoe to Block Island, one of the onter stations of the 

 Light-House Board, fnlly exposed, without intervention of land, to the 

 waves and storms of the ocean. 



On the southerly side of this island a light-house is about being erected, 

 and a siren station at this locality had been established and was in full 

 operation. 



There are here two sirens attached to one boiler, one to be used in case 

 of an accident to the other. For the sake of experiment they are of 

 slightly different qualities, one with a larger trumpet with a revolving 

 disk of the old i^attern, giving a lower tone; the o-ther a smaller trumpet, 

 having a revolving disk with openings allowing a much more sudden 

 full blast of steam, and revolving with greater velocity so as to give a 

 higher pitch. The latter is far the superior instrument, as was evident 

 to us by the sound which it produced, and as had been established by 

 the use of the artificial ear in the manufactory of Mr. Brown. The 

 effect on the unguarded ear was scarcely endurable, and the very earth" 

 around appeared to tremble during the blast. The keeper (an intelli- 

 gent man who has been promoted from the station of assistant keeper 

 at Beaver Tail light to this station) informed us that a fleet of fishing- 

 vessels coming in distinctly heard it at a distance estimated by their 

 rate of sailing at scarcely less than thirty miles ; this was on two sepa- 

 rate occasions. The keeper had been dkected to note and record the 

 date at which he heard the sound from other signals ; he reported that 

 he had frequently heard the fog-signal at Point Judith, a distance of 

 seventeen miles, and that the observer at the latter place frequently 

 heard his signal; but on comparing records the two sounds had not 

 been heard simultaneously by the two keepers ; when it was heard from 

 one station it was not heard from the other, illustrating again the gen- 

 eral rule that sound is not transmitted simultaneously with equal inten- 

 sity in opposite directions. 



This occasion also furnished very favorable conditions for observing 

 the remarkable x>henomenon of the ocean-echo. At the cessation of 

 each blast of the trumpet, after a slight interval, a distinct and pro- 

 longed echo was returned from the unobstructed ocean. It is important 

 to observe, in regard to this i)henomenon, that the siren is placed near 

 the edge of a perpendicular cliff, at an elevation of from 75 to 100 feet 

 above the ocean, and, furthermore, that the direction of the wind formed 

 an angle of about 35° with the axis of the trumpet. Xow, the loudness 

 of this echo was not the greatest at the siren-house, but increased in 

 intensity until a point was reached several hundred yards from the 

 trumpet, approximately' more in accordance with a reflection from the 

 waves. The wind was blowing from the shore with the direction of the 

 sound as it went off from the trumpet, and nearly against it on the re- 

 turn of the echo. I have attributed this phenomenon, which was first 

 observed in 18G6 at East Quoddy Head on the coast of Maine, and since 



