crowbar somehow got caught between the third rail and the track. A short circuit was established, and the electric fire spread across the entire electrified section of the yards. Submerged transmission cables were destroyed, fuses were everywhere burned out, and property worth some thousands of dollars was ruined. The meddler ran howling across the yards as if the very devil were indeed after him, and jumped over the edge of one of our deepest excavations. He was taken to the hospital with a broken leg. I hear that he has recovered since, but we have seen nothing further of him. As for the remainder of the gang, they were so thoroughly demoralized with fright that it took days to get them back to steady work. It was a costly accident, but it served a good purpose. There has been no loss of life or of property through trifling with the third rail since." ERECTING A SECTION OF THE TUNNEL LINING The electric locomotive looks as though two tenders had been detached from their engines and joined, back to back, by a box-like cabin. Both tenders are engines, and together are capable of developing 2,200 horse-power. In swiftness of acceleration and in ultimate speed the electric locomotive has surpassed the best type of steamengine as a drawer of moderately heavy passenger trains. It derives its power by shoecontact with the under side of the third rail, already described. Besides doing away with the smoke and gas generated by a steam-engine, it has the further advantage that, being a double-header, it is always in position to go forward, thus obviating the use of turn-tables, and making for economy both in yard space and in labor. It has been tested in all weathers and under all conditions that arise in practice, and has proved itself perfectly efficient. Only less important from the point of view of the transportation problem of New York than Sprague's invention is the invention of the English engineer Greathead, for it may be justly said that without the shield which he devised the great tunnels beneath the Hudson and East Rivers would have remained impossible. The story of the manner in which Greathead's inventive genius was brought to bear upon the traction problem of New York is an exceedingly romantic one. As early as 1879 a company of enterprising gentlemen concluded that tunnels must sooner or later supplant bridges as highways between Manhattan and the mainland. They decided that the best way to open the gates of New York was to burrow beneath the Hudson to the Jersey shore. With this object in view, they sank a brick shaft on the New Jersey side, and started to tunnel eastward. Their work workers, making their progress impossible. Undaunted, they decided to drive a temporary entrance or heading into the silt, from which to construct their tunnel tubes. This was accomplished by erecting, outside the air-lock, two rings formed of wrought-iron plates and angles, six feet four inches in diameter, four feet long, and bolted together. Then they ran a series of similar rings, each two feet six inches wide, and each succeeding one increasing about one foot six inches in diameter, until with the eleventh ring they reached the full diameter of the was watched with curiosity by all the world, for they were the first to attempt the construction of a great tunnel with the exclusive assistance of compressed air. When they had gone twenty-three feet below tide-level, they built an airlock into their brick shaft, from which they hoped the tunnel could be started. They decided to begin the break-up for the tunnel by opening the earth outward and timbering the roof of their excavation, while the sand or the rock or the silt of which it was composed was being removed and lifted to the surface. But the compressed air blew its way through the silt and permitted the water from the river above to filter down upon the projected tunnel. With the aid of compressed air, which held up the silt and water at the face of this improvised tunnel, they began their work of excavation and started the construction, within a thin iron casing, of a tubular wall of brick, the material of which their permanent tunnel was to be made. They had not gone far, however, when one of the rings of the improvised temporary tunnel, which led from the air-lock to the tube of brick, yielded to the pressure of the compressed air. The tunnel was flooded and wrenched out of shape by the inrushing water, and twenty men were drowned. The company attempted by many other fruitless experiments to BEHIND THE SHIELD IN THE PENNSYLVANIA TUNNEL "Your path is crossed by a circular diaphragm, a great steel disc dotted with doors and twenty-three feet high' " continue their work, but in 1882 they gave up their project under the conviction that subaqueous construction beneath so deep and heavy a river as the Hudson was impossible. In the meantime the population of Manhattan had grown so rapidly that what these pioneers had foreseen as a probable necessity had become a real one. In 1889 an English company, realizing that a sub-Hudson tunnel would be a valuable investment, consulted Sir B. Baker and Mr. James Henry Greathead. These gentlemen examined the abortive tubes beneath the Hudson, decided to substitute cast iron for brick as the permanent material of the tunnel, and devised a shield for its construction, those that are being used in the construction of the fourteen tunnels at present under way beneath the Hudson and the East Rivers. In looking at the Greathead shield one feels himself in the presence not so much of an instrument of steel as of a material embodiment of an idea. When the shield is set to work beneath the river, it represents the accumulated intelligence of the many men who have worked upon the problem of subaqueous construction for generations. In appearance the shield resembles a great drum built of heavy steel plates. In the drumhead, called the diaphragm, there are doors for the passage of workmen and the withdrawal of mud and rock and silt. ELECTRIC LOCOMOTIVE ON THE NEW YORK CENTRAL which was the first of its kind to be built in any part of the world. The construction of this shield was intrusted to Mr. E. W. Moir, who is at the present time vice-president of the concern that is building the great Pennsylvania tunnels under the East River. From the point of view of tunnel construction, it is of little consequence that the funds of the English company were soon exhausted, and that the tunnel beneath the Hudson was not completed by them. The shield which Mr. Moir constructed from Greathead's design was the most perfect realization of an idea which had been evolving in the minds of engineers since Brunel, the Frenchman, constructed the first crude shield for the tunnel which he built beneath the Thames in the early part of the last century, and it has served as the pattern for all the shields that have been built since, as well as for The upper drum rim is a cutting edge, which, when the shield is driven forward by hydraulic jacks, goes through the material in front like a biscuit-cutter, and holds up the river bed above while the biscuit of mud and silt is removed. The barrel of the drum, extending backward over the completed portion of the tunnel tube, forms the true shield for the men who set up the tunnel proper, ring by ring, within its protecting circumference. The bottom of the drum is at the same time the head of the completed tunnel tube, and is supplied with air-locks, through which workmen enter into the construction chamber within the shield. Immediately back of the drum-head there is a huge revolving crane called an "erector," also Greathead's invention, equipped with a muzzle like the jaws of an ant, which picks up the heavy sections of the tunnel rings, and, lifting them, TWIN TUBES OF THE PENNSYLVANIA TUNNEL IN PLACE UNDER THE RIVER holds them in place while the workmen dynamite without the aid of the shield. bolt them together. Few experiences are more impressive than a descent into one of the tunnels. You drop sixty feet or more beneath the surface of the ground to the level of the tunnel opening. If you chance to be entering the Pennsylvania tunnel, let us say, that has been driven at Thirty-second Street from the west side of Eleventh Avenue six thousand one hundred feet to the great shaft in Weehawken, you first pass through a long, circular cavern of rock which has been blasted out with As you advance towards the river you come to the subaqueous section in which the shield was used. Here your path is crossed by a circular diaphragm, a great steel disc dotted with doors, and twentythree feet high. At a little round window in one of these doors you see through the glass the eyes of a man. After some minutes. with a rush of steam, the door swings open, and a gang of men troop out. Now you enter this door with your guide, and find yourself in a small chamber, with benches at either side, like a |