The cable-driving apparatus is at the Brooklyn end of the bridge. Two sets of driving drums are provided, brit only one set is used at a time. The other stands idle, and its cable lies on the ties alongside the pulleys on which the live cable runs. In the street roads, using duplicate cables, duplicate sets of carrying pulleys are provided, because the men cannot get down into the conduit to put the spare cable on the pulleys. and tin ow the other one off when a change is made. This simple process of changing cables can be easily carried out on the bridge, however, as there is no cable conduit.
In all the New York cable roads the cable is driven by being wrapped around two 12-ft. drums, placed in nearly the same perpendicular plane, with their axes about 20 ft. apart. It is a curious fact that though the same cable runs around these two drums, they do not revolve at the same speed. In the bridge cable machinery one drum lags a revolution an hour be hind the other. This is supposed by some to be due to the fact that the cable slips or creeps more upon one drum than upon the other. Some engineers it is simply due to the unequal wearing of the drums, whereby one becomes of less diameter than the other. Inas much as it is always the same member of the pair that lags, the first hypothesis would seem nearer the truth. In the bridge machinery this is provided for by a system of automatic gearing• by which the two drums are geared to the driving shaft, much as two horses are hitched to a wagon by an equalizing bar.
From the opening of the bridge railway. September 24, 1883, to November 30, 1891, inclusive, 220,487.283 passengers were carried. Of the delays during the past year, 54 per cent. were occasioned by a failure or defect in some of the several parts of the cable-hauling machinery, and the other 46 per cent. by causes common to ordinary railroad transportation. The grip mechanism failing to act was the cause of but thirty delays, amounting alto gether to 2 hours and 57k minutes out of the 7.300 hours during which the cable was in motion.
Six cables have been used on the bridge. the two now in operation, and the four that have been worn out and thrown away. The following table gives the statistics in regard to them : The last column gives the average strain on the cable during use, and of course the ton miles are obtained by multiplying the weight pulled by the number of miles through which it was pulled. As the speed of the cable is constant, and also the distance traveled by each car between taking rip and releasing the cable, it is evident that the number of car trips per formed on any one cable will vary as the figures in the ton-mile column. These are nearly
constant. Cable No. 1, which ran the extraordinary distance of 228.329 miles, was gripped and released only a few more times than cable No. 4, which ran 74,000 miles—about the average life of a cable on a street railway. So it may be that the principal factor in the de struction of a cable is the pinching, crushing action of the grip jaws closing on it, and not its sliding through the grip or turning around corners. Of course this pinching action of the bridge grip is greater than that of the ordinary street-car kind, for the bridge cars are heavier, and the area of contact, being merely that of the point of tangency between a circle and a straight line, is less.
The Broadway Cable Road, of New York the present time of writing, a road 5.17 miles long is being built in New York City, extending from the Battery to Fifty-ninth Street. The track is set upon cast-iron yokes, which also hold the slot rails and encircle the ends of the sections of the sheet steel cable conduit. The yokes are 271 in. high to top of lugs, and 23 in. to rail seat. The distance between the yokes is 4 ft. 6 in. They rest upon separate foundations of concrete, which are 45 in. long, 18 in. wide, and 6 in. deep. The conduit in which the cable runs is formed of sheet steel sections, with a backing of concrete. The pits in which the carrier sheaves are located are 42 in. deep and 311 feet apart. The slot rail is formed of two like but oppositely arranged Z-shaped parts, leaving between them a groove, through which the grip extends from the car down into the conduit, where it engages the cable. The slot rails are braced at frequent intervals by wrought-iron rods pass ing through the tram rails and through the slot rails. The entire construction is designed to be permanent. The yokes which support the tracks weigh about 550 lbs. each ; the train rails weigh 91 lbs. per yard, and the slot rails weigh 67 lbs. per yard. Each was specially designed for this work. The gauge of the track is 4 ft. 8-1- in., and the distance from center to center of the tracks below Thirty-fifth Street is 9 ft.: above Thirty-fifth Street it is 10 ft. The diameter of the cables will be 14- in.; the cable drums will be 12 ft. in diameter ; the large rope-driving drums will be 32 ft. in diameter, and the small ones 10 ft. and 7 ft. 6 in. The Corliss engines driving these drums will have cylinders 36 and 38 in. in diameter, with a piston stroke of 60 in.
The following table of information relating to cable roads has been published by the Pacific Cable Railway Co.