SOUND-SIGNALS. 



731 



just as soon as the puff was noticed the engine was 

 stopped, and we waited for the sound. A very faint 

 sound was noticed up to four miles, and beyond that 

 nothing was heard. 



I was then on the point of returning to the rock to 

 examine the machinery personally, when it struck me 

 that I ought to go out to the estimated limit of the 

 range. On resuming our course, nothing was heard 

 until we were out seven miles approximately, when 

 the sound became audible again a clear, resonant 

 sound, but low-toned. We carried this characteristic 

 sound for another four miles, when it likewise disap- 

 peared. The engineer afterward told me that he car- 

 ried at least sixty pounds of steam. It was growing 

 late, and as the sea and rising winds gave promise of 

 a squall, we hurried back to get inside of the bar. . . . 

 The sea-captains on the iron vessels plying to San 

 Francisco reported later that they were able to hear 

 the sound at a distance of eight miles. . . . My im- 

 pression is that the cliffs of the east side are too far 

 distant to affect the sound one way or the other. I 

 have never heard an echo there, and I believe that the 

 distance is too great to have the noise of the surf upon 

 the rocky beach deaden the sound seaward of the sta- 

 tion. 



The ends of the trumpet are bent toward the hori- 

 zon, terminating in bell-shaped lips. The sound is 

 propagated therefrom in a horizontal plane, and pre- 

 vious experiments have shown that the sound pro- 

 duced is as strong as if the whole trumpet lay hori- 

 zontally. 



This is quoted as showing that the sound, 

 which on one occasion intermitted at two miles 

 from its source, was heard faintly at four miles, 

 and then again distinctly at seven miles, and 

 was carried out to eleven miles, when the 

 steamer turned back without ascertaining how 

 much farther the sound might be carried. This 

 is deemed a peculiar and important instance, 

 as there was practically no land or other thing 

 in front of the source of sound, unless it be an 

 opaque cloud from which the sound could re- 

 bound, or which could cast a sound-shadow for 

 hundreds of miles. 



Some curious experiments have taken place 

 off Whitehead Light and Fog-Signal Station, 

 which is in the Atlantic on a small island about 

 one and a half mile from the coast of Maine. 

 The fog-signal is on the southeastern slope of the 

 rock, and about seventy-five feet above mean 

 tide. The phenomena observed by Prof. Hen- 

 ry consisted in great variation of intensity of 

 sound while approaching and receding from 

 the station. One instance occurred during a 

 thick night-fog in 1872, when, approaching the 

 station in the steamer City of Eichmond at a 

 distance of six miles, the fog-signal, a ten-inch 

 steam-whistle, was distinctly heard and con- 

 tinued to be heard with increasing intensity 

 until within three miles, when the sound sud- 

 denly ceased to be heard, and was not heard 

 again until the steamer was within a quarter 

 of a mile of the station, though it was known 

 that the signal had been sounding during the 

 whole time. The wind was from the south, or 

 almost opposed to the sound, but daring the 

 whole of this time the fog-signal keeper could 

 hear the sound of the steamer's six-inch whis- 

 tle. 



Commander H. F. Picking, U. S. N., then in- 

 spector of the First Lighthouse District, having 



frequently received complaints from ship-mas- 

 ters that they lost the sound of the Whitehead 

 fog-signal, determined to ascertain the facts by 

 personal investigation, and in July, 1877, ap- 

 proached Whitehead from the southeast during 

 a fog. He reports that he heard the sound dis- 

 tinctly from six to four miles, then lost it, mul 

 could hear nothing until within a quarter of a 

 mile of the island, when the blast of the wins- 

 tie burst forth in full sound. The wind was 

 then against the sound. 



Previously, Gen. Duane, of the Corps of En- 

 gineers, U. S. A., then engineer of that light- 

 house district, reported that, approaching the 

 signal from the southwest, he heard the sound 

 at about six miles' distance, then lost it, and 

 did not hear it again until within about a quar- 

 ter of a mile. The wind was then also against 

 the sound. 



On Sept. 4, 1877, Prof. Henry made further 

 experiments at Whitehead. The weather was 

 clear, the wind west-southwest, with a velocity 

 of from ten to twelve miles, remaining nearly 

 constant during the day. The barometer stood 

 at 28-9 ; the thermometer at 67 Fahr. in the 

 open air, and about 67 in the water. As they 

 steamed from the station directly to windward, 

 the sound slightly diminished. When they were 

 between a quarter and a half mile distant, they 

 lost the sound completely, and it continued in- 

 audible for about a mile, when it was faintly 

 heard, and continued to increase in loudness 

 until they were four miles off, when it was 

 heard with clearness, but on going on it dimin- 

 ished gradually. They then went back over 

 their course, and observed the phenomena in 

 the reverse order. Experiments tried on three 

 other days showed curious results, which dif- 

 fered somewhat from those previously macie, 

 of which a full report is given in the " Annual 

 Report of the Lighthouse Board for 1877," 

 together with Prof. Henry's views as to the 

 cause of each observed phenomenon. A full 

 account of the matter is also given in the book 

 entitled " Henry on Sound." 



Col. C. E. Blunt, Corps of Engineers, U. S. A., 

 then engineer of the First Lighthouse District, 

 was also at a later date struck by the peculiar- 

 ity in the audition of the sound from this sig- 

 nal. Writing from Portland, Maine, on Sept. 

 28, 1882, he said: 



The peculiarities of Whitehead whistle have already 

 been noted. Quite recently I have myself noted one 

 of them. Leaving there for Portland, in the Myrtle, 

 early on the morning of the '2d instant, the \\ I. i>t It- 

 having been blown during fog part of the- previous 

 night for the first time, with its new characteristics 

 (4^-second blast and 26-sccond interval), the keeper 

 kept it going for a short time after the weather had 

 cleared, as I wished to test it. It was bright sun- 

 shine, with the light air from the southeast. I think. 

 Leaving the Head, the whistle was plainly heard for 

 two or three miles ; when, still in plain sight, the 

 sound began to grow fainter, and at length was quite 

 inaudible, though it was plainly blowing. In a few 

 minutes the sound was again faintly heard, and, in- 

 creasing in volume, soon came out in full force, and eo 

 continued. It was clearlv deflected upward, and then 

 downward, as I imagined, thus : 



