A Daboll trumpet is an air trumpet foghorn

Foghorn

A foghorn or fog signal or fog bell is a device that uses sound to warn vehicles of hazards or boats of the presence of other vehicles in foggy conditions. The term is most often used in relation to marine transport...

 which had been developed by an American

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, Celadon Leeds Daboll

Celadon Leeds Daboll

Celadon Leeds Daboll, , was a merchant in New London, Connecticut, and from 1854-1861 was employed in the U.S...

, of New London, Connecticut

New London, Connecticut

New London is a seaport city and a port of entry on the northeast coast of the United States.It is located at the mouth of the Thames River in New London County, southeastern Connecticut....

. It was basically a small coal-fired hot air engine

Hot air engine

A hot air engine is any heat engine which uses the expansion and contraction of air under the influence of a temperature change to convert thermal energy into mechanical work...

, which compressed air in a cylinder on top of which was a reed horn.

The Daboll trumpet, consists of a steel reed vibrating within a horn, which uses the hot air engine to force cold air by means of an air pump into a boiler, from which it escapes into the horn through a valve, causing the vibrations of the reed, which are regulated by an automatic cam.

Daboll's cousin, Charles Miner Daboll (1823-), inventor of the Daboll bushing, is credited with developing the Daboll trumpet for practical use.

The following citation is from: Scientific American Supplement, Vol. XIX, No. 470, Jan. 3, 1885.

The Daboll trumpet was invented by Mr. C.L. Daboll, of
Connecticut, who was experimenting to meet the announced wants of the
United States Lighthouse Board. The largest consists of a huge trumpet
seventeen feet long, with a throat three and one-half inches in diameter,
and a flaring mouth thirty-eight inches across. In the trumpet is a
resounding cavity, and a tongue-like steel reed ten inches long, two and
three-quarter inches wide, one inch thick at its fixed end, and half that
at its free end. Air is condensed in a reservoir and driven through the
trumpet by hot air or steam machinery at a pressure of from fifteen to
twenty pounds, and is capable of making a shriek which can be heard at a
great distance for a certain number of seconds each minute, by about
one-quarter of the power expended in the case of the whistle. In all his
experiments against and at right angles and at other angles to the wind,
the trumpet stood first and the whistle came next in power. In the trial
of the relative power of various instruments made by Gen. Duane in 1874,
the twelve-inch whistle was reported as exceeding the first-class Daboll
trumpet. Beaseley reports that the trumpet has done good work at various
British stations, making itself heard from five to ten miles. The engineer
in charge of the lighthouses of Canada says: "The expense for repairs, and
the frequent stoppages to make these repairs during the four years they
continued in use, made them [the trumpets] expensive and unreliable. The
frequent stoppages during foggy weather made them sources of danger
instead of aids to navigation. The sound of these trumpets has
deteriorated during the last year or so." Gen. Duane, reporting as to his
experiments in 1881, says: "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." Thus it
would seem that the Daboll trumpet is an exceptionally fine instrument,
producing a sound of great penetration and of sufficient power for
ordinary practical use, but that to be kept going it requires skillful
management and constant care.

"Congress made an appropriation in 1860 authorizing the Light-House Board to make
experiments with "Daboll's trumpet and other ear signals," but nothing was done until some time later."

Daboll's trumpet were installed at the following during trials:

• Cape Ann Light
  Cape Ann Light
  Cape Ann Light, is a historic lighthouse on Thacher Island, off Cape Ann in Rockport, Massachusetts.The Cape Ann Light Station is nationally significant as the last light station to be established under colonial rule and the first station in the United States to mark a navigational hazard rather...
  
  -Thatcher's Island ..... " June 30, 1869
• Execution Rocks Light-Long Island Sound Jan'y 25, 1869
• Monhegan Light-Manana Island (ME) Station April 4, 1870
• Boston Light
  Boston Light
  Boston Light is a lighthouse located on Little Brewster Island in outer Boston Harbor, Massachusetts. The first lighthouse to be built on the site dates back to 1716, and was the first lighthouse to be built in what is now the United States...
  
  -Boston, Mass Oct. 29, 1871
• Portland Head Light
  Portland Head Light
  Portland Head Light is a historic lighthouse in Cape Elizabeth, Maine that sits at the entrance of the shipping channel into Casco Bay. The headlight was the first built by the United States government, and is now a part of Fort Williams Park.-History:...
  
  -Portland, Me Nov., 1871
• Montauk Point Light-Long Island May 1, 1873
• Highland Light-Cape Cod June 23, 1873

Sources

• "Improved Fog Signal," New York Times, Oct. 26, 1866.
• Scientific American Supplement, Vol. XIX, No. 470, Jan. 3, 1885.
• "Light Station Components," National Park Service. http://www.nps.gov/history/maritime/ltcomp.htm