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Silver-plating brushes.-Used to clean the lamp, clockwork, and uten

sils.

Sash-brushes.-Used to paint the iron work of the lanterns and illuminating apparatus.

Bottle brushes.-Used to clean the burners and chimneys.
Wick-boxes. For preservation of wicks of various sizes.
Oil-gauge. For measuring height of oil in butts.

TESTING INSTRUMENTS.

This is a

Photometer, used for measuring the intensity of light. modification of Bunsen's instrument. The intensity of a light is ob tained by comparing it with a light of a known standard, which in the United States Light-House service is a London sperm candle burning about 2 grains of its substance per minute. For lights of great intensity the candle is first compared with a larger light, and then this latter with the light to be tested. This instrument consists of a graduated scale, at the two extremities of which are placed the lights to be compared. The graduation of this scale is made according to the formula based upon the law that the intensity of a light varies inversely as the square of the distance at which it is seen. Upon the scale slides a small white screen, placed vertically between the two lights. In the center of this screen a circular hole about half an inch in diameter is closed by a piece of thin paper rendered translucent by a solution of sperma ceti in oil of turpentine. The screen is so placed between two mirrors, that a reflection of the two sides can be seen at the same moment and compared. To test the lights, the screen is moved to a position between them where the two images on the screen are exactly of the same brightness. An index gives the reading of the scale at this point, and this shows the intensity of one light in terms of the other.

All oil used by the light-house establishment is subjected to a careful test before purchase. The experiments are made in a dark room, the ceilings, walls, and floors of which are painted dead black.

An artificial ear, designed by the chairman of the Light-House Board, consisting of a large trumpet-shaped instrument with a membrane stretched tightly over the smaller end, which is covered with a glass shade having a magnifying glass in its upper portion. Sand is placed on this membrane, and when two sounds are to be compared, the agitation of the sand, when the large end is towards the direction from which the sound comes, is noted in each case. The arrangement of the particles of sand is also noted to find the nodal points of the sound. This instrument is intended to merely concentrate the rays of sound and not to act as a resounding cavity. The distance when measured in feet or yards gives the number indicating the penetrating power of the sound under trial.

LIGHT-HOUSES. AND MODELS.

Model of caisson and coffer-dam-Used in building the foundation for Spectacle Reef light-house, Straits of Mackinac.

Model of Spectacle Reef Light house. This light-house stands upon a reef in the northern end of Lake Huron, off the eastern end of the Straits of Mackinac. It is built upon the southern end of the most northerly of two shoals of limestone, paved with a covering of bowlders 2 feet thick. The least water in the shoals is about 7 feet; but at the site selected for the light-house the rock is 11 feet under water. The nearest land 10 miles distant is the southeasterly point of Bois Blanc Island; a depot was made for building materials at Scammon's Harbor, about 16 miles from the light-house site. The greatest exposure to waves is to the southeastward, from which direction the seas have a fetch of about 170 miles.

Were there no other elements of destruction, no unusual precautions would have been necessary to secure sufficient stability. But under certain meteorological conditions currents having a velocity of from 2 to 3 miles per hour are developed here, and during the inclement season serve to move to and from ice fields 2 feet thick, which frequently have an area of thousands of acres. This fresh-water ice is of great solidity, and, when moving in masses, and with the velocity named, has a force almost irresistible. The aim was to oppose to it a structure against which the ice would be at first crushed, and then so impeded in motion as to cause it to ground upon the shoal itself, thus forming a barrier against subsequent action. In the spring of 1875 the ice was piled up against the light-house 30 feet above the water, or 7 feet above the sill of the doorway, which is 23 feet above the lake. When the keepers went to the station to exhibit the light (not in operation during the winter) they were unable to obtain entrance to the tower until they had cut a passage through this pile of ice to the doorway. The tower is built of light-gray limestone, and is 97 feet from base to focal plane. The illuminating apparatus is of the second order, showing alternate. red and white flashes at intervals of thirty seconds, visible 17 miles. The fog-signal is a 10-inch steam whistle.

Model of Brandywine Shoal light-house on Brandywine Shoal, Delaware Bay. This light-house is erected on iron screw piles, with an iron screw pile ice-breaker. The illuminating apparatus is 46 feet above sea-level, and is of the third order, showing a fixed white light visible 12 miles. The fog-signal is a bell struck by machinery.

Model of Coffin's Patches light-house.-An iron pile structure on the Florida Reefs, with a first order illuminating apparatus visible 19 miles. Model of Sand Key light-house.-The original is on a small sand and shell island in the Florida Reefs, and is 7 nautical miles from Key West, Fla. It is an iron pile light-house 121 feet from base to focal plane, with a first order illuminating apparatus showing a clear light

for one minute followed by a brilliant flash of ten seconds, preceded and followed by partial eclipses of twenty-five seconds' duration.

Model of light-house at Chicago, Ill.—The light-house is an iron tower on the north pier of Chicago Harbor, Lake Michigan. It is 83 feet above the lake level, and has an illuminating apparatus, fixed white, of the third order, visible 16 miles.

Minots Ledge light-house.-On the outer Minots, Boston Bay, an exceedingly exposed and dangerous situation. The tower is built of darkgray granite, 100 feet from base to focal plane, and 92 feet above the sea-level. It has a second order fixed white illuminating apparatus, and is visible 16 miles. The fog signal is a bell struck by machinery. The original tower (an open-work iron structure) was destroyed about twenty-five years ago.

Model of the crib work for the foundation of Southwest Pass light-house, mouth of the Mississippi River.—This is built on a low marshy islaud west of the pass. In the construction of this model, the two upper courses of grillage and plank floor were omitted. The model is made from a log which it is known had been sunk in Lake Pontchartrain for more than

50 years.

Complete light-house, fitted up, with light-keepers in charge.—This lighthouse, in which a keeper lived during the exhibition, has a fourth-order lens, flashing red and white alternately, and was lighted every evening during the exhibition. This iron structure is to be permanently placed on the caisson on Ship John Shoal, Delaware River, at the close of the exhibition.

BUOYS (OUTSIDE OF THE BUILDING).

First-class iron can buoy,
First-class iron nun buog.
First-class iron spar buoy.
First class iron spar buoy.
Second-class iron can buoy.
Second-class iron nun buoy.
Second-class iron spar buoy.

Second-class iron spar buoy.
Third-class iron can buoy.

Third-class iron nun buoy.

All these buoys had attached ballast balls, chains, sinkers, &c., complete for service, and were so painted as to show the different marks and colors used in the buoy service.

INSIDE OF BUILDING.

Models of spar buoys in use.

Models of iron spar buoys (experimental.)

buoys:

Class.

The following description table was also shown in connection with the

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Complete model of light ship No. 40.-This model is rigged to represent a light-ship ready for service on her station, on a scale of three-quarters of an inch to the foot. Its timbers, planks, &c., are on exact scale, and each one is placed in position separately and is drawn off on board as in the mold loft.

Lantern for the mast-head of a light-ship with lamps and reflectors.
Day-mark for the mast-head of a light-ship.

Mushroom anchor for a light-ship weighing 4,200 pounds.

BOOKS, MAPS, PLANS, AND GRAPHIC REPRESENTATIONS.

The drawings and paintings are as follows:
Currituck Beach light-house, North Carolina.
Saint Augustine light-house, Florida.
Race Rock light-house, Long Island Sound.
Cleveland, Ohio, light-house, Lake Erie.
Piedras Blancas light-house, California.

Ship John Shoal light-house, Delaware River.

Hunting Island light house, South Carolina.

Thimble Shoal light-house, Hampton Roads, Virginia.

First Class light-vessel, with steam fog-signal.

Screw-Pile River and Harbor light-house.

Sand Key light-house, Florida.

Alligator Reef light-house, Florida.

Pigeon Point light-house, California.

Craighill Channel light-house (front), Chesapeake Bay.
Craighill Channel light-house, (rear), Chesapeake Bay.
Fort Sumter light-house, South Carolina.
Light-house tender.

Weight.

Grosse Point light-house, Lake Michigan.

Fowey Rocks light-house, Florida.

Day-beacon, sea, Flower Reef, Long Island Sound.

Minots Ledge light-house.

Penfield Reef light-house, Long Island Sound.

Spectacle Reef light-house, Lake Huron.

Foundation for Cross Ledge light-house, Delaware Bay.

Tybee Island light-house, South Carolina.

Old Field Point light-house Long Island Sound.

Fowey Rocks light-house, Florida.

A large map 17 feet by 19 feet.-This shows the location of each light under the jurisdiction of the Light-House Board. Each class is distinguished on the chart by the size of the red circular spot denoting order and its range of visibility.

The following table shows the number of the lights shown on the chart, and their respective orders:

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The Light-House Board's Reports for 1873, 1874, and 1875, also lighthouse lists, buoy lists, and special reports, were issued, on request, to persons interested in light-house matters. A set of portfolios and books were also exhibited, showing specifications, plans, and designs for the following lights:

Calcasien, Louisiana.
Cleveland, Ohio.

Day-beacons for Potomac River.
West Point, New York.
Keeper's dwelling for first-order
steam fog whistle.
Oil butts.

Iron bell-boat.

Fourth-order harbor light and keeper's dwellings.

Hudson City, New York.

Hunting Island, South Carolina.

Thirty mile Point, Lake Ontario.
Block Island, Rhode Island.
Thimble Shoal, Virginia.
Penfield Reef, Long Island Sound.
Craighill Channel, Iron Beacon.
Buoys, sinkers, &c.
Fowey Rocks, Florida.
Southwest Ledge, Long Island
Sound.

Thomas Point Shoal, Chesapeake.
Timbalier, Louisiana.

Body's Island, North Carolina.

FOG SIGNALS.

Fog-bell struck by a large hammer worked by clock-work.-It gives one,

two, one, three strokes at regular intervals.

The clock-work was de

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