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act approved amount annual report appropriation August beacon bell Board boat boiler Boston building built buoys cable Cape carried changed channel coast completed condition construction consumed cost depot direction distance district dwelling east Engineers entrance erected established estimated February feet fixed flash fog signal front Harbor Head heard inches increased iron Island June keepers Lake lamps land lantern Ledge lens light-house light-ship light-station light-vessel Little Maine March mark Michigan miles Myrtle navigation needed observations operation passing placed Point position post lights pounds range recommended Reef renewed repairs replaced River Rock running seconds September ship Shoal shown shows side siren sound South station steam steam whistle steamer structure supply tender therefor tion tons of coal tower trumpet various vessels wharf whistle wind York
Page 283 - ... miles from the station, the fog-signal, which is a 10-inch steam-whistle, was distinctly perceived, and continued to be heard with increasing intensity of sound until within about three miles, when the sound suddenly ceased to be heard, and was not perceived again until the vessel approached within a quarter of a mile of the station, although from conclusive evidence, furnished by the keeper, it was shown that the signal had been sounding during the whole time.
Page 282 - The most perplexing difficulty, however, arises from the fact that the signal often appears to be surrounded by a belt, varying in radins from one to one and a half miles, from which the sound appears to be entirely absent. Thus, in moving directly from a station, the sound is audible for the distance of a mile, is then lost for about the same distance, after which it is again distinctly heard for a long time.
Page 295 - ... will tend to diverge down to it, and throw off secondary waves, or, as I shall call them, diverging waves, so as to reconstitute the gap that is thus made. These secondary waves will be heard as a continuation of the sound, more or less faint, after the primary waves are altogether above our heads. [This phenomenon of divergence presents many difficulties, and has only as yet been dealt with for particular cases. It may, however, be assumed, from what is known respecting it, that in the case...
Page 283 - It is evident that this result could not be due to any mottled condition or want of acoustic transparency of the atmosphere, since this would absorb the sound equally in both directions. The only plausible explanation of this phenomenon is that which refers it to the action of the wind. In the case of the sound from the steamer, the wind was favorable for its transmission, and hence it is not strange that its sound should be heard on the island when the sound from the other instrument...
Page 143 - TWELFTH DISTRICT: Includes all aids to navigation on Lake Michigan, Green Bay, and tributary waters lying west of a line drawn across the Straits of Mackinac just east of Old Mackinac Point Light Station, Mich.
Page 234 - Nothing can be more beautiful," says Mr. Alan Stevenson, " than an entire apparatus for a fixed light of the first order. It consists of a central belt of refractors, forming a hollow cylinder, 6 feet in diameter and 30 inches high ; below it are six triangular rings of glass ranged in a cylindrical form, and above a crown of thirteen rings of glass, forming by their union a hollow cage composed of polished glass, 10 feet high and 6 feet in diameter. I know of no work of art more beautiful or creditable...
Page 250 - The Daboll trumpet, operated by a caloric engine, should only be employed in exceptional cases, such as at stations where no water can be procured, and where — from the proximity of other signals, it may be necessary to vary the nature of the sound.
Page 282 - In the foregoing I differ entirely in opinion from General Duane as to the cause of extinction of powerful sounds being due to the unequal density of the atmosphere. The velocity of sound is not at all affected by barometric pressure, but if the difference in pressure is caused by a difference in heat, or by the expansive power of vapor mingled with the air, a slight degree of obstruction of sounds may be observed.
Page 282 - The full significance however of this idea did not reveal itself to me until in searching the bibliography of sound, I found an account of the hypothesis of Professor Stokes in the Proceedings of the British Association for 1857,* in which the effect of an upper current in deflecting the wave of sound so as to throw it down • upon the ear of the auditor, or directing it upward far above his head, is fully explained.