ship the greater is the number per unit of its vibrations, and the longer the steamer the greater is the corresponding time of its vibrations. Different parts of the hull of a vessel show different degrees of vibration in the water; that is to say, the shake varies in intensity at different points in the length of the hull. There are places where it is excessive, and places, termed "nodes," where it does not exist.

The use of shifting weights for the trimming of vessels is in common use, and has been for many years, though chiefly on river and Sound steamers. In some cases the weight is shifted by mechanism, but a more common method is to make use of boxes containing iron weights, such as chain cables. The boxes are mounted on wheels, and when the boat begins to roll, the seamen, on signal from the pilot, move the weight as required to bring the boat back to an even keel. Quite a number of patents have been granted in this country for self-acting ballastshifting devices, with pendulums to trim or prevent vessels from rolling.

The deep-sea thermometer, as invented abroad and improved by officers of the United States Navy, is really a self-registering instrument, so arranged that it is automatically turned upside down when brought up, the effect being to break the column of mercury, while enough remains in the tube's upper end to measure temperature at moment of inversion.

The aurophone is an invention which has been called a "steamship's ears." Its object is to enable the lookout to locate and determine the directions from which sounds come at sea.

The solorometer, an invention by Lieutenant Beehler, of the United States Navy, is a new method of determining the position of a ship at sea with accuracy and quickness,, and it practically supersedes the sextant.

The Sextant. The sextant is an instrument for measuring the angular distance of objects by means of reflection. The principle of its construction depends upon the theorem that if a ray of light suffer double reflection, the angle between the original ray and its direction after the second reflection is double the angle made by the reflect

ing surfaces. It consists of a It consists of a graduated limb, forming about the sixth part of a circle, (whence the name sextant); two mirrors to reflect the rays of light coming from the objects under observation; a telescope, which collects and transmits to the eye the rays of light; an index and a vernier, placed at the extremity of an alidade, to read on the graduated limb the quantity of which the large mirror has turned. When observing altitudes, the instrument is held perpendicularly to the horizon, in observations in the plane of the line joining the two objects. In taking noon observations at sea, to determine the lati tude, the observer takes his place shortly before meridian, and turning down one or several of the shades, to prevent his eye being injured by the glare, directs the telescope or sight-tube to the sun, moving the index so as to bring its reflected image to coincide with the sea horizon; as the sun rises, he gradually advances the limb, clamping it and using the regulating screw for this purpose, as the sun's path becomes more nearly horizontal, and slightly rocking the instrument from side to side to insure that it is in a vertical plane at the moment when the sun attains his greatest height. The reading of the limb. at the moment when the sun begins to dip is noted, and a very simple calculation, adding his declination derived from the Nautical Almanac to the true zenith distance obtained by observation, gives the latitude.

A novel arrangement for signalling at sea during fogs has been placed in position on Winter Quarter Lightship, No. 45. Two oil engines supply compressed air to two upright boilers, which are automatically acted upon by timeclocks, by which the whistle valves are opened and closed every 55 seconds. Explosions of oil vapor take the place of steam and give shrill blasts.

Baron d'Alessandro, a Frenchman, some years ago invented an appliance to take the place of oil on the water. It consisted in covering the surface of the sea with a specially prepared insubmergible and imputrescible thin netting, which does not rise above the surface or offer resistance to the wind, and has the effect of a bed of oil in stilling waves and rendering navigation safer.

There is a tide-indicator on the wharf at Fort Hamil

ton, New York Harbor. Inside a small building is a self-registering gauge. Over it, above the building, a tidal indicator is displayed in a semicircle, with eight figures marked on it from 1 to 6, looking like half the dial of a clock. A pointer turns about the center of the circle and indicates the tide in number of feet by pointing to these figures.

Admiral Makaroff, of the Russian Navy, advocated building buffers or false noses for vessels, with a view to deaden the effect of a shock in case of collision at sea. The idea is to allow the bow to be sharp and yet so constructed that it shall collapse and present a flat surface when it strikes another vessel.

Among the inventions which had a practical trial during our war with Spain, was a French device for stopping shot holes, called the Colome's Stopper. One of these was employed to close a rent made by a shell in the battleship Iowa. The hole was about a foot above the waterline. As soon as it was inserted, the inflow ceased. The stopper consists of a rod having at one end an iron plate, pivoted at the centre so that it can be folded backward along the rod. When used the plate is placed outward through the hole and turned, a cellulose cushion is placed upon the rod and by aid of a nut forced tightly against the side of the ship (within) over the hole. They are of various sizes to suit the size of the hole.

An English mechanical genius devised a method of indicating and stopping a leak by the use of compressed air. The ship is divided into airtight compartments, into which lead different tubes from the compressors. Should a vessel "spring a leak," the indictator will show which compartment is affected, so that the compressed air may be forced in to drive the water out.

One of the most ingenious and effective devices for lifesaving is the breeches buoy, for bringing people ashore from stranded vessels. It is simply a pair of canvas breeches with a circular life-preserver attached, into which the person on shipboard gets. When the tackles are drawn out by means of ropes from the shore, the breeches buoy is sent out over the ropes and brought back by the life

savers.

In 1874, Lieutenant Brunel, of Dieppe, introduced pocket life-saving lines, weighing complete five ounces, of which a great many have been used in France. Around a wooden float 90 feet of stout cord is wound, which terminates in a grapnel.

Among the inventions for life-saving apparatus is the pneumatic gun for throwing a line to ships in distress. The air is admitted from a reservoir to the chamber behind the projectile at a pressure of 2,400 pounds to the square inch. An improved pneumatic gun was accepted by the Government for use, in 1899, so light that it can be adjusted from a lifeboat.

The lower part of a curious device resembles a lifepreserving dress with two legs into which the shipwrecked person can get, the upper part being a kind of buoy or floating chamber, provided with a hood. There is some chance of freedom of motion of head and arms. In the upper part can be placed provisions and water enough to last several weeks.

- A Paris scientist has invented an apparatus by which with the aid of a magnesium flash-light, arranged to work under water, he has taken instantaneous pictures at the depths ordinarily attained by submarine divers. He has also made photographs at a depth of nearly 20 feet with the aid of sunlight alone, the time of exposure being extended to 30 or 40 minutes.

Paper bottles are said to be about to supersede glass bottles on shipboard, as they cannot be broken in rough weather and expensive wines and liquors lost. They are a German invention and are made water-tight in a solution which is the inventor's secret.

An Austrian engineer has made extensive experiments at Fiume, Austria, of his invention by which the steamship Clotilte, 2,000 tons, when running 12 knots an hour was brought to a standstill within 30 seconds, and before she had traversed 40 feet, in spite of the engines still working. This marine brake can be applied to any ship.

J. W. Worcester, of Newark, invented a fish-tail propeller. Instead of revolving as in the ordinary propeller, the fins, two in number, oscillate in a small radius, and steer as well as propel the boat.

J. Ferguson, of London, has invented a propeller which can be sheathed or withdrawn within the hull at a moment's notice. When not in use it is invisibly housed in a tube fixed in the stern post. Extending rods operated by a lever bring the propeller outside the boat with blades folded together, and a second lever unfolds the blades and places them in position.

The induced draught apparatus invented by a Mr. Martin, after trials in the gunboat Gossamer, was definitely pronounced a success; as greater speed was attained and less horsepower used than when the boilers were driven by forced draught. The stokeholds were cooler, as well, a great consideration in warm climates.

The proposal to sheathe ships with copper coated with mercury is attracting attention. The idea is that such an arrangement would effectually prevent barnacles from adhering to vessels' bottoms.

Up to the present time, electricity has scarcely been thought suitable as the principal motive power or propelling power for the larger type of vessels. This is undoubtedly owing to the fact that for a given horsepower a triple or quadruple expansion steam engine would take up less space, and probably weigh less than an electrical installation of equal power. Storage batteries are out of the question for such uses, although persons not well up in electrical subjects frequently wonder why our ocean greyhounds are not propelled by some such method. A vessel requiring an average of 10,000 horsepower to propel it across the Atlantic, and displacing 5,000 tons, would be obliged to carry, were storage batteries alone made use of, 324,480,000 pounds of such batteries, or 162,240 tons, which would be 30 times as much as the ship weighed for motive power alone.

The United States Government has been for some years developing electric apparatus for use on shipboard. This policy serves as a vast experimental school for the training of electrical experts, and affords a stimulus to electrical invention. Uncle Sam's vessels have more elaborate and effective electrical appliances than those of any other nation. There are electric lights in place of lamps, electric motors in place of hoisting, pumping and other