subjected to, and the weights get dangerously near the bottom of the shaft.

The smaller weights are conveniently constructed as shown in Figs. 395 and 396. Each one is provided with two handles, a a, has a hole through the centre b, and a loose wedge-shaped piece, c, which when removed allows each weight to be slid on the rope without moving any of the others. This piece, c, is not only wedge-shaped in plan, but also in cross-section, and cannot drop out of place when the weight is in a horizontal posi

tion. The blocks weigh about 165 lbs. each, and can be handled by two men.

Weights are objectionable at the bottom of any shaft from which water has to be lifted by a tank, or in which dirt accumulates. In the latter case, sooner or later the space beneath the weights gets filled up with mud, and the guides become slack. Weights also occupy considerable space; they cannot be made large in diameter, and consequently have to be correspondingly long. They must also hang some distance above the bottom in order to allow for the extension of the guides by expansion. Consequently, if water

Figs. 395 and 396.

has to be drawn by tanks on the cages, only a short portion of the space below the inset can be cleared out, as the cages cannot go past the top of the weights. When the sump-room is limited this is an important matter, and it becomes necessary to adopt some method of tightening the guides as will allow the cage to practically travel on to the bottom of the shaft.

There are several ways of doing this. In all, buntons of suitable strength are first fixed at the lowest point in the shaft, and the bottom ends of the guides firmly secured thereto by glands or eyebolts, the upper ends being carried to bearers on the pit frame. Stretching screws passing through the top bearers and fixed to the guides provide the easiest means for tightening, but have no elasticity, and do not allow for expansion or contraction. In some cases an unequal armed lever is fixed on the headgear; one end is weighted and the other is attached by a sliding collar, beneath a gland on the conductor. Stops are inserted to prevent too much travel, but sufficient play is allowed to provide for the working stretch of the guide. This method is effective, but occupies considerable space, and is unsightly. A preferable arrangement has been designed by Cocker Bros, consisting of two strong springs in a case. These cases, which consist of two parts, the body a, Figs. 396a and 3966, and the cap, b, are fixed on a beam in the headgear over each conductor. The body is hollow to receive the springs, c, and the cap, b, slides easily over and rests upon the springs which project above it. The conductors are attached to a screw-ended main bolt, d, which passes vertically between

the springs through both body and cap, and is secured by a nut on the outside. Upon the outside of both the cap and the body are corresponding lugs, f and g, projecting from opposite sides, and

between these lugs supporting bolts, hh, can be temporarily placed, their lower ends resting in recesses, and their upper ends, which are screw-threaded and provided with adjusting nuts, ii, passing into holes through the upper lugs on the cap. When these bolts are in the position illustrated, they act as pillars or supports, and stop the cap from pressing on the springs while the initial slack is being taken out of the conductors by screwing up the main bolt, d. After this is accom

plished, the supporting bolts, h, are withdrawn by slacking the nuts, i, and the cap allowed to rest upon the springs, c, which are about 20 inches long and have about 5 inches compression in each. Should any undue strain come on the guide, the cap compresses the springs until it rests on the body of the case, and thus damage by excessive overloading is prevented.

Conductors between Cages.-The only objection urged against wire guides, is that the clearance between the cages has to be more than if a rigid conductor was employed. For deep shafts this is, no doubt, true, if the guides are connected to the cage on both sides; but a method is used which entirely removes the disadvantage, and allows the cages with wire conductors to be safely worked with as little clearance as if rail or wood guides were employed. In ordinary cases three conductors will be fixed to each cage, but in the special method two other ropes are suspended down the shaft in between the cages and not connected with either of them. These latter ropes are often flat ones, and at the point of meeting may be lined with steel strips passing from one to the other, while the cages are lagged up on the inside. The result of the whole arrangement is that from the top of the shaft to the bottom, the cages are on opposite sides of the central conductors, and cannot possibly catch each other when passing.

Guide Shoes.-Some connection has to be made between the cage and the guides, so that the former shall travel correctly along the latter. If the guides are of wood, the shoe need not encircle them, and the form shown in Fig. 397 is employed. With iron rail guides, which are also rigid, the common form of shoe has already been illustrated in Fig. 385, but with a view of reducing resistance, rolling has been substituted for sliding friction, and at Anzin Colliery, France, the guide shoe is composed of two wheels, one on each side of the rail guide (a a, Fig. 398), revolving on a pin bolted to the side of the cage.

For wire ropes, which are flexible, the guide shoe must go completely round them, or any oscillation would throw the slipper off

the guide. A common mistake is to make the shoes very much stronger and heavier than necessity requires. If the guides are properly hung, and the centres of the shoes set to the correct gauge, very little strain is thrown on them, and only a comparatively weak connection is required. It is advisable that renewable bushes should be provided for the parts gripping the rope, as all the wear takes place there. A good form is shown in Fig. 399. It consists of a base plate, a, bolted to the cage by two pins, bb, and has cast-iron bushes, c, divided into halves, these being fixed to the base plate by a steel strap, d, which encircles them. This strap is kept in position

by two pins, ee, also bolted to the sides of the cage. By taking out these two latter pins, the bushes can be changed whenever desired without removing the base plate. As an experiment, the author tried brass bushes, but the result was by no means satisfactory. The first

a

Fig. 399.

cost was much more than that of cast-iron ones, and their life was considerably less. If the guides are kept well lubricated the wear is slight.

Guide Troughs.-While the cage is travelling in the shaft a small amount of oscillation is not objectionable, as there is seldom less than from 6 to 12 inches clearance at the corners, but when passing through the timber framing at the top, or at intermediate hangingon places, where the clearance space is small, additional means have to be provided to prevent the cage from deviating from a definite line. With rigid guides nothing is necessary, but with wire ropes the general plan is to place a trough opposite each guide at the point where they pass through the frame. The usual construction is to rivet two strips of angle iron to a plate at the back; the angle pieces are belled out at the top and bottom ends of the trough, and the back plate is bent outwards to avoid any chance of the slipper receiving a blow when it enters the trough as it is gradually guided into the proper groove. The troughs are held in position by bolts which pass through the timber framing.

Where the banking level is a considerable distance above the

ground, it is by no means a rare occurrence, when storms prevail,. for the guides to be blown out of the troughs, and if this happens. during winding a serious accident may result. Mr. A. B. Southall has designed a simple appliance, which entirely gets over the difficulty. The troughs consist of two wooden rods (a a, Figs. 400 and 401) con-nected together by iron strap plates, b. Two iron strips, c c, arefastened by bolts having countersunk heads to each wooden rod on the inner side and extend its entire length. The guide rope d passes. through a small block, e, nade in halves and provided with a projection on each side which fit into the recesses on the inner side of the trough (Fig. 401). This block is free to move upwards, but is prevented from dropping completely out of the trough by a stopplate, h, placed at the lower end. In its normal position it rests against this stop-plate, and as the guide passes through a hole in the centre, it is always locked in its proper position in the trough. When. the slipper of the cage reaches this block, it lifts it upwards, but on the descent of the cage the block, by the action of gravity, drops into its former position.

Engines. For winding purposes a pair of engines, with the cranks set at right angles, is the only form admissible. There are, however, two ways of placing these engines, either vertical or horizontal. Vertical engines are becoming things of the past. In the first place the cost of foundations is great. The drum of a winding engine may weigh anything up to 80 tons, and if such a mass has to be placed 30 to 40 feet above the ground, and revolved at a high velocity, the structure carrying it must be correspondingly large. Vertical engines were designed to reduce wear in the pistons, it being considered that if a large cylinder

was placed horizontally, the lower half would wear very fast. For the same reason, with horizontal engines it was usual to employ back piston-rods, but both in this case and in the former one, the evil has been proved by experience to be more imaginary than real, and as a result, both vertical engines and back piston rods are being abandoned. At Harris Navigation Colliery, inverted engines are applied at one pit -that is to say, the drum is placed below and the cylinders above. The cost of foundations is reduced, but it would appear that no real benefit has resulted, as the second pair of engines at the same colliery are placed horizontally.

The all but universal practice is to make the engines direct actingthat is to say, the piston rod is coupled direct through the connectingrod to the crank keyed on the shaft on which the drum is placed.

The valves regulating the admission and discharge of steam to and from the cylinders are worked by eccentrics, either on, or driven off, the drum shaft. The reversing gear is generally one of the wellknown forms of Stephenson's link motion, and is controlled through an arrangement of levers, links, and a horizontal shaft, by a vertical handle placed near the engine driver.

The design and strengths of the various parts is more a matter for the mechanical than the mining engineer. The stroke is usually made twice the diameter of the cylinder, and the connecting-rod three times the length of the stroke. The valves, both steam and exhaust, should be of large proportions. In winding, everything is sacrificed to speed. The engine should be simple, easily handled, and, above all, over its work. On large engines, the double beat, or Cornish valve, has been the one generally adopted, owing to the ease with which it is capable of being moved, but improvements in the design of equilibrium slide valves have brought these types into favour. Corliss valves are employed on recent compound winders.

The proper size of engine to do a given amount of work may be easily found by applying a very elementary formula of mechanics, but simple as the problem is, the determination of the required size is often more a matter of guess-work than of reasoning. In moving a load, an engine has to do two things, and every one is aware that a greater expenditure of force is required to start a load than to keep that load in motion when once started. The greatest work that a winding engine has to do, is to get a given mass into a certain velocity uniformly accelerated from rest, and to raise the load the distance passed over during the time this velocity is being obtained.

The following formula which has been contributed by Mr. H. G. Graves is based on such reasoning, and will be found satisfactory :— W = the whole weight in lbs set in motion-i.e., all cages, ropes, tubs, coal, and one-half of the drum and pulleys.

*

L = the unbalanced loads in lbs -i.e, coal and the average length of rope unbalanced, if any, between the start and point of maximum speed.

v = greatest velocity attained in feet per second, uniformly accelerated from rest.

t = time in seconds during which v is obtained.

g= gravity = 32.2.

P = average pressure of steam in the cylinders in lbs. per square inch.

A

total piston area in square inches.

number of feet of piston travel in time t.

The work done in foot-lbs. by the engine in time t in setting the whole mass in motion and in lifting the unbalanced load is :—

The work in foot-lbs. yielded by an engine in the time t is the product of the total steam pressure and the distance through which it is exerted. By equating these amounts, the following formula is obtained :

This assumes that all the weight of the drum and pulleys is concentrated at the rim. In reality, the weight and velocity at the radius of gyration should be considered.