onds less than was required in the specifications under which it had been constructed. Colonel Hodges pulled the switch again, and the return journey was made in the same manner and time. Since then other gates have been swung in other locks with like success, and there has been no "crash" -save in the reputation of the prophet who, like all his kind, concealed his identity at the moment of supreme inspiration.

In addition to the fender chains and double gates, other protective devices will be in readiness for use when canal operation begins. The most elaborate of these is a ponderous-looking structure called the emergency dam. In repose on the walls at each entrance to the upper locks, it resembles an iron railway bridge. It is in fact a steel truss bridge of the cantilever type. It is so placed that it can, in emergency, be swung across the lock entrance in two minutes. If such an extreme improbability should occur as the carrying away of the fender chain and the double gates of an upper lock, allowing the waters of the lake to rush in and flood the lower locks, carrying destruction through them, the emergency dam can be swung across the channel, and through the application of its ingenious devices the rush of water can gradually be checked. First, a series of wicket girders will be lowered into the channel and their ends will drop into iron pockets in the concrete lock floor. Down the runways in these girders, steel plates will be lowered one by one, in tiers, building a dam from the bottom upward, and diminishing progressively the flow of water until a complete barrier is erected.

The question is raised frequently as to the sufficiency of the Gatun Lake water supply for the operation of the canal in case of an exceptionally small rainfall. It should be borne in mind that during eight or nine months of the year the lake will be kept constantly full by the prevailing rains, and consequently a surplus will need to be stored for only three or four months of the dry season. The smallest run-off of water in the basin during the past 22 years, as measured at Gatun, was that of the fiscal year 1912, which was about 132,000,000,000 cubic feet. Previous to that year the smallest run-off of record was 146,000,000,000 cubic feet. In 1910 the run-off was 360,000,000,000 cubic feet, or a sufficient

quantity to fill the lake one and a half times. The low record of 1912 is of interest as showing the effect which a similar dry season, occurring after the opening of the canal, would have upon its capacity for navigation. Assuming that the Gatun Lake was at elevation plus 87 at the beginning of the dry season on December 1, and that the hydro-electric plant at the Gatun spillway was in continuous operation, and that 48 lockages a day were being made, the elevation of the lake would be reduced to its lowest point, plus 79.5, on May 7, at the close of the dry season, after which it would continuously rise. With the water at plus 79 in Gatun Lake there would be 39 feet of water in Culebra Cut, which would be ample for navigation. The water surface of the lake will be maintained during the rainy season at 87 feet above sea level, making the minimum channel depth in the canal 47 feet. As navigation can be carried on with about 39 feet of water, there will be stored for the dry season surplus over 7 feet of water. Making due allowance for evaporation, seepage, leakage at the gates, and power consumption, this would be ample for 41 passages daily through the locks, using them at full length, or about 58 lockages a day when partial length is used, as would be usually the case, and when cross-filling from one lock to the other through the central wall is employed. This would be a larger number of lockages than would be possible in a single day. The average number of lockages through the Sault Ste. Marie Canal on the American side was 39 per day in the season of navigation of 1910, which was about eight months long. The average number of ships passed was about 11⁄2 per lockage. The freight carried was about 26,000,000 tons. The Suez Canal passed about 12 vessels per day, with a total tonnage for the same year of 16,582,000.

The canal will be lighted from end to end by electricity and gas. Here and there along its course, high up on the hillsides and in cleared spots in the jungle, are visible concrete light-houses which seem curiously out of place. These are for the range lights of the channel, which are to be used in all sections of the canal save in Culebra Cut, where beacons will be substituted as being more practicable. Electricity will be used wherever accessibility

will permit, but in the floating buoys which will mark the channel through Gatun Lake, and in towers and beacons in inaccessible places, compressed acetylene dissolved in acetone will be used. The candle-power of the range lights will vary, according to the length of the range, from about 2,500 to 15,000. The most powerful lights will be those marking the sea channels at the Atlantic and Pacific entrances, they being visible from about 12 to 18 nautical miles. The beacons and gas-buoy lights will have about 850 candle-power. White lights will be used throughout, and, in order to eliminate the

possibility of confusing the lights with one another and with the lights on shore, all range lights, beacons, and buoys will have individual characteristics formed by flashes and combinations of flashes of light and dark intervals.

The brilliant spots in the illuminated canal will be at the locks, where great clusters of electric lamps, high up on shapely concrete columns, will flood every portion of the vast structure with noonday brightness, making them the shining centres and symbols of what Joseph Pennell calls the greatest of the world's Wonders of Work.

IN

I. THE GREAT GATES TO THE LOCK CHAM

BERS [frontispiece to this number] The gates to the lock chambers are immense steel structures, 7 feet thick and with two leaves each 65 feet wide. They open from the centre, swinging back against the lock walls, the powerful machinery operating them as easily as a parlor door is opened or closed. While appearing solid, they are in reality a great steel "honey-comb" structure covered with heavy steel plates. The gates, like the locks, are the same throughout the entire canal.

II. WHERE THE CANAL CROSSES THE CORDILLERAS

Nothing could be truer than the statement that "the canal workers have removed mountains." Where the canal crosses the Cordilleras a great ravine had to be excavated in order to allow the water from Gatun Lake to flow through to the locks at Pedro Miguel.

III. CULEBRA CUT, LOOKING NORTH FROM CONTRACTOR'S HILL

Looking north from Contractor's Hill a wonderful view of Culebra Cut is obtained. To the right is a slide, started in January. This view shows clearly the step-by-step method of excavating.

IV. THE CULEBRA CUT BEFORE THE CUCARACHA SLIDE OF JANUARY, 1913 The excavating of Culebra Cut was the greatest undertaking in the building of the Panama Canal. It is nearly 9 miles long and has a channel width at the bottom of 300 feet. Beginning where the Chagres River flows into the canal, the cut varies from 75 to 160 feet in depth for a distance of 6 miles. Through the foot-hills of the Cordilleras, the Great Continental Divide, the excavation is much deeper, until at "Contractor's Hill," where the canal goes through the Great Divide, it is 500 feet from the top of the cut to canal bottom. Near by, the hillside, as far upward as the reddish earth, comprises the great Cucaracha Slide. It covers nearly 50 acres, and about 6,000,000 cubic yards of material from it has gone into the canal prism. The photograph was taken before the heaviest developments of the slide occurred.

V. AT WORK IN CULEBRA CUT

The great work of excavating has literally been done step by step, for while the steamshovels are working at one level, others are digging and loading from another elevation. Trains of from 20 to 30 cars, drawn by powerful locomotives, remove the dirt and rock dug and loaded by these shovels.