the track at frequent intervals by the flagman of passenger-trains at night whenever the train is not making schedule time between telegraph-stations.

A train finding a fusee burning upon the track must come to a full stop, and not proceed until it is burned out.

Train Signals.

Each train, or engine without a train, while running after sunset, or during the day in foggy weather, must display the white headlight in front of the engine, and two red lights in the rear of the train or engine, except shifting-engines in yards, which will display two green lights instead of red.

Each passenger-train while running must have a bell-cord attached to the signal-bell of the engine, passing over or through the entire length, and secured to the rear end of the train.

Each passenger-train while running must display one green flag at the rear by day, and two green lights, one at each side of the rear car, at night, as markers, to enable operators and enginemen to know that the whole of the train is attached to the engine.

Each freight-train while running must display two green flags by day, and two green lights at night, one on each side of the rear car, as markers, to enable operators and trainmen to know that the whole of the train is attached to the engine.

Two green flags by day, and two green lights at night, carried in front of an engine, denote that the engine or train is followed by another engine or train running on the same schedule. The engine or train thus signalled will be entitled to the same schedule rights and privileges as the engine or train carrying the signals.

Two white flags by day, and two white lights at night, carried in front of an engine, denote that the engine or train is extra. These signals shall always be displayed by all work and extra trains or engines, except when running as a regular train.

A blue flag by day, and a blue light by night, placed in the drawhead or on the platform or step of a car, at the end of a car stand

ing on the main track or sidings, denote that car repairmen are at work underneath the cars. The car or train thus protected shall not be coupled to, or move until the blue signal is removed by the car repairmen.

Enginemen's Signals.

One short blast of the whistle is a signal to apply the brakes Stop. Thus,

Two long blasts of the whistle is a signal to throw off the brakes. Thus,

Two short blasts of the whistle when running is an answer to signal of conductor to stop at next station. Thus,

Three short blasts of the whistle when standing is a signal that the engine or train will back. Thus,

Three short blasts of the whistle when running is a signal to be given by passenger-trains, when carrying signals for a following train, to call the attention of trains they pass to the signals. Thus,

Four long blasts of the whistle is a signal to call in the flagman or signalman. Thus,

Four short blasts of the whistle is the engineman's call for signals. Thus,

Two long followed by two short blasts of the whistle when running is the signal for approaching a road crossing at grade. Thus,

Five short blasts of the whistle is a signal to the flagman to go back and protect the rear of the train. Thus,

A succession of short blasts of the whistle is an alarm for cattle, and calls the attention of trainmen to danger ahead.

A blast of the whistle of five seconds' duration is a signal for approaching stations, railroad crossings, and draw-bridges.

Conductors' Signals.

BY BELL-CORD.

One tap of the signal-bell when the engine is standing is a notice

to start.

Two taps of the signal-bell when the engine is standing is a notice to call in the flagman.

Two taps of the signal-bell when the engine is running is a notice to stop at once.

Three taps of the signal-bell when the engine is standing is a notice to back the train.

Three taps of the signal-bell when the engine is running is a signal to stop at the next station.

Signals by Lamp.

A lamp swung across the track is a signal to stop.

A lamp raised and lowered vertically is a signal to move ahead. A lamp swung in a circle is a signal to move back.

The Screw-Propeller.

The screw-propeller, so commonly applied to the propulsion of vessels, consists of two, three, or four helical or twisted blades set upon a shaft, or axis, revolving beneath the water at the stern. Experience has shown that no screw-propeller, designed or invented up to the present time, has proved superior to all others for all ships. The best propeller for any vessel is the one best suited for that model, regardless of the number of blades, diameter, or pitch. The principles of screw-propulsion embrace those relating to hydraulics also, so that, in proportioning the screw, the lines of the hull should be considered.

The pitch of the screw is the distance that it would advance in one revolution, if working in a solid, fixed nut; or it is the distance between the threads measured in a line with the shaft. The

pitch of a screw, or the circumference of a paddle-wheel, multiplied by the revolutions, and two figures cut off for decimals, gives the speed in knots per hour.

The term left-handed propeller means a screw with a left-handed thread, and a right-handed one has a right-handed thread. A lefthanded propeller, to move the ship ahead, goes from left to right, while a right-handed one turns from right to left, looking from the engine-room towards the stern of the boat.

The force which drives a vessel forward when a screw-propeller is used, is the pressure exerted against the thrust-block. Steam being admitted to the cylinder, causes the piston to move, and the motion being transmitted through the connecting-rod to the crank-pin, crank, and propeller shafts, causes the latter to revolve, by which the pressure it exerts against the water is transmitted to the thrust-block, and the vessel forced forward.

The term "slip of the screw" means the difference between the actual advance of the propeller through the water, and the advance which would be accomplished, if there was no recession of the water produced by the pressure of the propelling surface. A screw of 15 feet, if working in a stationary nut, would advance 15 feet for every revolution; but when it acts in the water, it may only advance 14 feet or less, the difference being caused by the water being pressed back, owing to its inertia being inadequate to resist the moving force. In such cases the slip is said to be 1 foot in 15, or nearly 7 per cent. loss.

Measurement of the screw-propeller.-The surface of a screwpropeller is the same as would be generated by a line revolving around a cylinder, through the axis of which it passes, and at the same time advancing along the axis. To find the area of a propeller-shaft, square the diameter, and multiply by the decimal, .7854.

The Errickson and Delameter propellers are those most generally used, although the Loper Screw, as it is termed, is frequently employed, but it has now nearly gone out of use.

The thrust-block of a propeller is formed of a series of rings,

generally of brass, with spaces between them, into which an equal number of solid collars fit. The thrust is exerted against the fore and aft faces of these rings and collars.

The stern-tube is a tunnel located in the dead wood of a ship, in which the propeller-shaft revolves. Its outer end is made water-tight by a stuffing-box containing a fibrous packing. Stern-tubes were formerly made of wood, but they are now generally made of boiler-plate.

The Paddle-Wheel.

The advantages of the paddle-wheel as a motive-power depend on the amount of the immersion. When the water approaches the centre or reaches above it, it is obvious that great waste of power will ensue. It is quite as obvious that the greater the diameter of the wheel the greater the leverage, and the greater is the effect obtained.

The slip of the paddle is caused by the recession of the water from the buckets, or it is a retrograde motion given to the water in a line parallel to the direction in which the ship is moving. The slip of the wheel is the difference between the speed of the ship and that of the wheel. The amount of slip is determined by finding the speed of the ship in feet per hour and subtracting it from the speed of the wheel at the centre of pressure, or centre of action, in feet per hour.

of

The centre of action is that point in a wheel in which the effect would not be altered if the whole action of the water were concentrated. The centre of action may be thus determined: Lay down the wheel to a certain scale and line off the dip on it. Take of the breadth of the totally-immersed paddles and the depth of those partially immersed, and add them; their sum divided by the number of paddles partially or totally in the water will give the distance of the centre of action from the edge of the floats. This distance subtracted from the radius of the wheel and multiplied by 2, will give the diameter of the centre of action of the wheel. The dip of the wheel is 69 inches, and, at that dip, there are 7 full-immersed floats and one immersed