favor that a large number of underground slopes are now operated by engines located at the surface; the rope being conveyed through a pump-slope, breast, travelling-way, or airway, or air-shaft opening at the surface, or even through a bore hole.

A bore hole six inches in diameter and about six hundred feet deep was lately drilled at the Hollenback colliery to be used for this purpose.

When the power is supplied by an engine located at the surface this objection to the use of a single rope disappears. At the Wyoming colliery, near Wilkes-Barre, two inside slopes are thus operated through the air shaft.

When the power is obtained from an engine run by steam inside the mine, the disposal of the exhaust steam is a problem similar in every respect to that incident to the employment of steam pumps underground.

In addition to trouble from the exhaust, there is necessarily more or less loss from radiation and condensation.

A partial solution of this problem has been effected at some collieries by the substitution of compressed air for steam, not only for the slope engines but also to run the pumps.

At collieries in which there is a considerable amount of rock-work, (tunnel driving, etc.,) which may be more cheaply and quickly done with power drills, there can be no question as to the expediency of erecting air-compressing machinery to supply the place of steam at the inside pumps and slope engines; but when no work of this class is needed, and there is perhaps only one inside slope engine, the cost of erecting and maintaining a compressing plant would doubtless be greater than the saving effected by increased life of mine timber, etc.

This subject is now receiving much attention from mine operators and engineers. It must be thoroughly studied in all its bearings and in the light of carefully prepared statistics before it will be possible to determine in advance whether, in the case of any particular working, compressed air can be advantageously substituted for steam.

Underground slope engines and drums do not differ from those in use on the surface, and at a large number of inside slopes the winding plant consists of old machinery that has been used at the surface.

As a chamber must be excavated in the coal above the gangway to hold the winding machinery, and as it is often difficult and never advisable to make this engine-room very large, large drums are seldom used.

The engines are generally small and geared to the drum by second or third motion. As the output from any one inside slope is seldom very great, the necessity for fast winding and first motion engines does not exist.

The engine and drum are often bolted to a frame of heavy sills, held in place by being notched and wedged into the rib on each side of the engine-room, and in some cases sunk in trenches hewed in the floor.

Atlas Sheet No. IX illustrates a dirt plane designed to raise cars from two different levels at Breaker No. 10 of the

Lehigh Coal and Navigation Company. The engine is located a short distance above the upper truck-pit, and the ropes are carried up on bearing pulleys to horizontal sheaves at the head of the plane.

The ropes are wound on two drums placed side by side. on the same shaft. The diameters of these drums bear the same ratio with the lengths of lift on each side of the plane, so that when a car has been raised to the top on the long lift, the barney on the opposite side has descended into its pit, and vice versa.

This drawing also shows the arrangement commonly used when the cars are raised by a barney. The barney (ram or truck) is a small car running on rails inside of the main track, which descend into a pit at the bottom, so that the car may be run in over the barney to the foot of the plane.

Hinged latches (bridges) are shown at the landings above both of the barney-pits, by which the empty cars are run off the plane at a sufficient vertical distance above the foot of the plane to allow the empty cars to be run to the breaker and return (loaded) to the foot, by gravity. When a car is

being raised these latches are lifted to allow the cars to pass beneath them.

Plans similar to this might be used on slopes for raising coal from two different levels at the same time, but the adoption of such a complicated system is open to many objections.

Prominent among these is the fact that such a winding plant resembles a compound windlass, and if one side of the plane is very much greater than the other, the weight of the empty car and rope on the long side will raise the loaded car through the upper part of the lift.

It is evident that when it becomes necessary to lengthen either side of such a plane, the relative diameters of the drums must be altered.

Difficulty will also doubtless be experienced from unequal wear of the lagging on the two drums, altering the ratio between their diameters.

Gravity plane.

A gravity plane fitted with horizontal sheaves (instead of a drum) is shown by Atlas Sheet No. X. This plane is located at the Lehigh Coal and Navigation company's No. 8 colliery.

As the drawing clearly shows the details of this plan, it is not necessary to give any further explanation of its construction.

It will be observed that the rope after turning around the large sheave runs over the smaller sheave and back to the main sheave, making two turns; that the large sheave is controlled by a brake, and that the rope passes through counterweighted slides (stops) which produce sufficient tension to prevent the rope from slipping after the car is detached at the top.

The advantages of this method of replacing the drum and two ropes by sheaves and a single rope will be considered in the chapter on winding machinery.

In the arrangement of tracks this plane differs from any of the plans described in other portions of this report. It

consists of four rails to within a few feet of the bottom, where a central rail replaces the two inside rails, and a few feet below this the three rails are merged into a single track. By reference to Fig. 37 it will be seen that this is simply a modification of that plan.

CHAPTER XIII.

Rolling Stock and Motive Power.

Mine cars of a size almost unknown in other mining districts are in use throughout the anthracite regions. In English mines the trams or mine cars rarely hold forty or fifty cubic feet, and in the coal-mining districts of Continental Europe larger mine cars are rarely seen.

In American bituminous mining practice larger cars are used, but cars even approaching in size to some in use in the anthracite regions could be taken into very few bituminous mines.

The present large size of anthracite mine cars is due to the great thickness of the seams now being worked, and to the ready adaptation by our mining engineers of the knowledge, gained by the long and dearly-bought experience of railroad managers, that freight can be more cheaply loaded, transported, and handled in large than in small cars.

Several conditions, without which such large cars could not be economically used, have favored to an unusual degree the use of very large cars:

1. Thickness of the beds worked.

2. Steep dip of the beds allowing the cars to be loaded by gravity; and increasing the possible height of the gangways in seams of moderate thickness.

3. Gaseous condition of the mines necessitating large gangways for thorough ventilation.

In height the cars are necessarily limited by the height of the gangways; and in flat workings by the thickness of

the bed.

In width they are limited by the width of the gangways. In length by the wheel base and by the sharpness of the mine road curves.

The length seldom exceeds ten feet, the width five feet, and the height (from the rail) five feet and a half.

(203 AC.)