498 RESEARCHES IN SOUND. 



the macliinery, and also in regard to any obstacle which might interfere 

 with the propagation of the sonnd, the keeper was directed to put the 

 instrument in operation and to continue to sound it for at least two 

 hours, or until the steamer was lost sight of, which direction was com- 

 plied with. In i^assing from the island, almost directly against a light 

 wind, the intensity of the sound gradually diminished as a whole, with 

 the increase of distance, but varied in loudness from blast to blast, 

 now louder, then again more feeble, until it finally ceased at a distance 

 of about fifteen miles, as estimated by the intervals between the blasts 

 and the sight of the steam as seen through a spy-glass, and also from 

 points on the Coast-Smvey charts. 



The result of this investigation clearly showed the power of the appa- 

 ratus in i)ropagating sound under conditions not entirely favorable, 

 since the wind, though light, was in opposition to the sound. 



Cape Elizahetli Light- Station, Maine, August 29, 1873. — The fog-signal 

 at this place is on a prominent headland to which the course of all ves- 

 sels is directed when bound from the southward into Portland Harbor. 

 It is furnished with two light houses 910 feet apart and 143 feet above 

 sea-level. The easterly- tower is connected with the keeper's dwelling 

 by a wooden-covered way 200 feet long and about 12 feet high 5 the 

 station is fui^nished with a 10-inch steam fog-whistle, placed to the 

 southward of the easterly tower, at a distance of about G25 feet and 

 about at right angles with the covered way ; it therefore has a back- 

 ground, including the covered waj', of about 65 feet above the height of 

 the whistle, which was found to reflect a perceptible echo. The whistle 

 was actuated by steam at 55 pounds pressure, consuming from GO to 65 

 pounds of anthracite coal per hour. The w^histle itself differs from the 

 ordinary locomotive-whistle by having a projecting ledge or rim around 

 the lower part through which the sheet of steam issues to strike against 

 the lower edge of the bell. What effect this projecting ledge or rim may 

 have is not known to the observers. This whistle is provided, (for the 

 purpose of concentrating the sound in a given direction,) with a hollow 

 truncated iDyramid 20 feet long, 10 feet square at the large end, and 2^ 

 feet square at the small end, the axis of the pyramid being placed par- 

 allel to the horizon, with the whistle at the smaller end. In order to 

 ascertain the effect of this appendage to the whistle the simplest plan 

 would have been to have noted the intensity of sound at various points 

 on a circle of which the whistle would have been the center. This being 

 impracticable on account of the intervention of the land, the observations 

 were confined to points on the three arcs of a circle of about 120c>, of 

 which the axis divided the space into 80° and 40° and a radius of one, 

 two, and three miles. The result of these observations was that, starting 

 from the axis of the trumpet on the east side, the sound grew slightly 

 less loud until the prolongation of the side of the trumpet was reached, 

 when it became comparatively faint and contiiiued so until the line be- 



