sufficiently. These are made of hoop iron, or flat bar iron, screwed down the pattern sides. They are turned over at the lower end, and have a lifting eye at the top to receive the

Fig. 92.-Lifting Straps.

hooks of sling chains. They may be screwed on the face simply, A, or let in flush and screwed, B.

Lift Pump. Sometimes called the common, suction, or atmospheric pump. It depends for its action on the pressure of the atmosphere. The principle is shown in Fig. 93. A is the cylinder or barrel in which the hollow bucket B works up and down. At c is a valve only opening upwards. D is another valve sometimes distinguished by the name "suction valve," opening similarly. The valves are prevented from rising too high by the arch of the bucket in one case and by the stop piece at E in the other case. The bucket is made airtight by leather or other packing.

When the bucket is raised the air in the lower part of the barrel is rarefied; consequently the valve D is pushed up by the water below, which enters to fill the partial vacuum. As the bucket descends, the suction valve closes, and the bucket valve opens to allow of the escape of the air under compression. Thus the air becomes more and more exhausted at each stroke until water only fills the cylinder. Water then flows through the valve D at each up stroke, and through c at each down stroke, and as the piston is raised, the water above it will be forced through the discharge pipe.

There is of course no "suction" in the operation. The water rises owing to the weight of the atmosphere. It follows, therefore, that

the lift pump cannot raise water to a greater height than that of a water barometer, or 34 ft. But it is impracticable to place the suction valve at a greater height than 26 ft. above the

level of the water in the well, owing chiefly to leakages past the valves and defects in fittings.

The pull on the pump rod at the upward stroke is equal to the weight of a column of water with base equal to the cross sectional area of barrel, and having a height equal to that of the water being raised, reckoned from the level in the well.

Fig. 94 shows a lift pump of a different type, crank-driven, using cranks of two or three throws. The barrel A is of brass, or in many cases of iron, brass-lined. The bucket в has a retaining ring c for the leather, with a central boss and ribs attached, and screwed up to the end of the rod. The valve D lifts against the pressure of a coiled spring and abutment piece. The foot valve E lifts against a similar spring, the abutment piece of which is screwed into

Lifts. Designates any rooms or cages which are elevated and lowered in a perpendicular, or an inclined direction. They are used for goods of all kinds, and passengers, are actuated by hand, by steam, water, and electricity.

Belt-driven lifts, actuated from a steam or gas engine, were formerly more common than any others, the small endless rope, hand operated, for light lifts only excepted. They are still largely employed, though their place has been invaded by other agencies. The drive is by a fast pulley with loose pulley adjacent, and the rope is coiled round a drum. The connection between the two is made by a worm and worm wheel. A hand brake is fitted, the cage is counterbalanced by a cast-iron weight, and runs between guides of hardwood, or of iron. The cage is of the suspended type.

The hand-power lift is raised and lowered. by an endless rope running in pulleys with vee grooves, and actuating spur gears. A hand brake is fitted. It is used for passengers and for light goods in warehouses. Such lifts are made in capacities ranging from 2 to 10 cwt.

An important detail of any suspended lift used for passengers is the provision for safety in case fracture of the ropes should occur. Many patents have been taken out for these.

The

Waygood's safety gear acts by the pressure of cams on the wood runners which guide the movements of the lifts. In this the ropes are led down from the top corners of the framing to the bottom of the cage, and attached to a sliding plate-a kind of equalising lever which is maintained in position by the weight of the cage and the tension of the ropes. cams, four in number, are attached to this plate, two at each end, and connected by shafts passing beneath the cage. Should a rope or ropes break, the cams are drawn inwards simultaneously, and grip the wood runners between which the cage moves. In the improbable event of all four ropes breaking, a fifth rope is fitted. This carries no weight unless all the other ropes fail, in which event the strain comes upon this rope, which, being attached directly to one of the cams, would pull on all four and hold the cage up.

Automatic Lift Gates.-It is now common to fit such gates to "Fool-proof" service lifts, so

that none but the authorised attendant at the service floor is able to control the opening and closing of the gates. From this floor the box can be dispatched to any floor desired. But on the opening of the door the apparatus becomes locked, so that the box cannot be moved till the door is closed. The automatic closing of the door is the means whereby the box is returned to the serving floor. There is also a safety gate lock added by the Easton Lift Co. to their car switch, or push button controller, which renders it impossible for the attendant to start or move the lift until all gates are closed and locked. A. Smith & Stevens also make a lock of this character, but in which the gate must be absolutely locked before the current is put on.

Electric Drives. -Electric lifts in one system are driven and reversed directly by a reversing motor, which is started, stopped, and reversed with each journey of the cage. No current is consumed when the cage is not working, but the original outlay is greater than with a continually running motor.

In the other system the motor runs continually and is belted to a countershaft, whence other belts drive the lift in opposite directions. Current is wasted while the lift is idle, and the noise of a countershaft would be objectionable in many buildings.

In high-speed electric lifts provision has to be made in the winding of the motor, and the design of controller for rapid acceleration of speed, and a large range of variable speeds without shock.

A compact design of electric lift drive is that in which a motor drives a worm directly, and a worm wheel to a rope drum or sheave.

Ropes. In the drum drive, a separate set of ropes is used for the suspension of the cage, and of the counterbalance weight, each set being anchored to the drum. The car ropes are being wound on while the balance weight ropes are being unwound, and vice versa. The drum is therefore grooved to carry a length of rope equal to the height or travel of the lift. It is preferable, as in cranes, to make the drum with right and left-handed threads from the centre to the ends, to maintain the lift centrally, instead of following the lateral traverse of

the ropes. Two ropes are used for the lift, and two for the balance weight.

To avoid the lateral traverse of ropes on a drum, and the need for a slack cable required with a drum drive, a sheave drive has been substituted, having vee grooves.

The ropes are not attached as to

drums, but the car is attached to one

end of the ropes, and the balance weight to the other, and the ropes are driven by the friction of the vee grooves. The vee drive was introduced by Messrs Smith & Stevens many years ago for winding engines with steel ropes. The object sought was to obtain greater safety by preventing the over-winding which so often occurs with the drum machine. The safety is due to the slackening of the ropes in the vees when the balance weight or cage reaches the bottom. The question of traverse on the drum was a secondary consideration. It has been stated that this design causes more wear on the ropes than the drum drive does. But on the point of wear and tear of ropes, opinions differ considerably. Messrs Smith & Stevens have employed both vee and drum in winding engines and for lifts for many years, and find that vee wheels do not wear out any more quickly, provided grooves and ropes are suitably made.

In the Easton cross-over drive four suspending ropes are used on an eight-grooved sheave, with grooves turned to the radius of the ropes, so avoiding the friction inseparable from vee grooves. The

four suspending ropes are first laid over half the circumference down to a four-grooved jockey pulley just below, and having its axis set at a slight angle with that of the main pulleys. Thence the ropes are again led round the second set of grooves on the driving pulley. The ropes are smaller in diameter than when two are used, and it is found that their wear is about equal to that of ropes on drums.

on the cam shaft, throws gripping cams into operation on both sides of the cage.

Hydraulic and Electric Lifts.-In comparing the relative economies of hydraulic and electric lifts, regard must be had to the circumstances of each case. The choice must often depend on which kind of power is already installed, and on the relative costs of each when an installation has to be made. For low lifts and

heavy loads the hydraulic should generally have the preference, but for contrary conditions the electric scores.

One reason for the economy of the electric over the hydraulic lift is that due to counterbalancing. The car is counterbalanced by a suspended weight, so reducing the maximum load on the motor. If the counterbalance is increased to include the average live load carried in the car, then the motor will only have a light duty to perform. On the other hand, the hydraulic cylinder must be filled at each stroke, regardless of light loads.

Many figures prove that though the first cost of hydraulic lifts is less than that of the electrically-driven ones, yet the expenses of operating them are very materially greater, current costing less than high-pressure water, and much less than water from low-pressure mains. It has not been proved that electric lifts cost more for repairs than hydraulic ones do. But a greater argument in favour of electric lifts is that most large buildings and works now include an electric lighting plant, and this can be extended to include the lifts more cheaply than to lay down an hydraulic plant for them. One man can also better look after an electric plant, than both electric and hydraulic.

Lighthouse.-A tower-like structure, built on a dangerous coast or islet to give warning of danger to vessels.

Lighthouses are built of iron, masonry, or concrete. Iron plates resembling tank plates are bolted together by their flanges, and the joints caulked. Window and door frames are made of gun-metal. Staircases are of spiral form, of cast iron. But such a structure would not be strong enough to withstand the lash of the sea in exposed situations. Here masonry is used, the stones of which are joggled together. Of late years concrete has been largely invading the province of masonry. There are several examples of light framework of cast columns, and wrought-iron braced structures.

The illuminating apparatus has been highly elaborated. The earlier lights were fixed, as are many now, but large numbers are revolving, which enables lights at different spots to be distinguished from each other, and

also largely increases the power of the beam. Another method of distinguishing lights is making them occulting; in this system the lens is of the ordinary fixed type, but by a mechanical arrangement the light is periodically covered or extinguished, thus producing an intermittent character of light. The earlier methods of reflection were catoptric, denoting metallic reflection. Modern lights are dioptric, in which glass is used for reflection and refraction, in which case about 25 per cent. of light is saved; and the catadioptric, in which both glass and metal are employed. The term holophotal denotes the condensation of an entire sphere of rays from a lamp into a single beam, without wasteful reflection and refraction. The occasion for the numerous designs of lenses and prisms lies in the necessity for condensing the rays that would be dispersed in upward and downward directions, which is accomplished by arrangements of prisms above and below the main lens, which bend those rays downwards and upwards respectively. The spread of the rays is not interfered with in the horizontal direction in a fixed light, but these have to be coerced in a revolving light. The displacement of the parabolic catoptric reflector has been due to the Fresnel dioptric system, which includes lenses, refractors, and prisms. In 1822 Fresnel designed a lens built up of rings, the centres of curvature of which receded from the axis according to their distance from the centre. This device had the effect of eliminating the spherical aberration of a solid lens. Fresnel's cylindrical refractor was glass hoop for rendering the rays parallel in a vertical plane. Fresnel's reflecting prisms were designed for reflecting rays horizontally. His refracting prisms refract the rays which fall on them in one plane. The foregoing in various combinations have been embodied in most modern illuminating apparatus. These, with improvements effected in the lamps themselves, by Fresnel and others, have produced designs suitable for all conditions.

a

Oils have been, and are used largely for lamps. The wicks are arranged in concentric circles. A single large lamp has been substituted for several separate lamps. Electric arc lamps have entered into rivalry with