The forms for the interior face of the side walls consisted of a heavy steel frame with steel face plates which were moved into position. The full height of the wall for the length of the form was then constructed, whereupon the form was moved to the next section. The cost of concrete on the Gatun locks was $6.64 per cubic yard in 1911 and $7.76 in 1912.

For the Miraflores locks broken stone was brought from a very large quarry opened high up on the side of Ancon Hill, where a satisfactory quality of stone was found. About 5,000 cubic yards of stone were turned out daily. Heavy blasts were set off above the berm, and steam-shovels then loaded the material into railroad dump cars, which were switched farther down the hill by locomotives to the top of a crusher, and were dumped directly into it. "Dobe" shots were fired off in the cars to split the stones which were too large. The crusher could take stones equal in size to that of an ordinary chair. The crushed material was screened, and that of proper size was carried by rubber belt to a sorting-screen and passed into the storage bins underneath for the various sizes. The material from the large crusher which was rejected by the screen passed into four small gyratory crushers, and from these on to the same belt for transfer to the sorting-screen. With this efficient and well arranged plant the cost of stone delivered at the site of the locks was about $0.82 per cubic yard.

Sand for the Miraflores Locks was obtained by dredging at Chamé and was transferred by barges to Balboa, where it was excavated by means of grab buckets and was placed in overhead storage bins for transfer by rail to the lock site. The total cost in storage at the locks was about $0.76 per cubic yard.

To handle the stone and sand in building the Miraflores Locks, an elevated trestle was built parallel to the locks and about 200 feet away. The cars dumped the stone on the side toward the locks, and the sand on the side away from them. On the bank between the locks and the storage pile a large cantilever crane operated on a track. The tower contained bins and hoppers and two large concrete-mixers. One cantilever arm overhung the storage piles, and a grab bucket kept the bins full. The other cantilever arm overhung the nearest lock wall and transferred the concrete from the mixers to the lock wall. The cement was taken directly from the cars to the tower without first going into

FIG. 12.-Miraflores upper locks, general view, looking north from lower locks. Steam-shovel excavation for lower locks in foreground. November 8, 1911.

FIG. 13. Concrete-handling cranes at Miraflores. The booms on the right carry the buckets which pick up the sand and stone from the storage piles and dump in bins over the mixers in center of crane. The booms on the left carry the concrete for dumping in the lock walls.

storage. In the lock chamber was another cantilever crane, which transported concrete to those parts of the lock beyond the reach of the mixing-crane. The entire plant is probably one of the most perfect ever devised for handling concrete. The cost of the concrete in place was $4.68 in 1911 and $4.77 in 1912, per cubic yard.

LOCKS AS THE LIMITING Feature.

The locks fix the maximum-size ship that may use the canal. They will pass the largest now built or building, but will not, for instance, pass the floating dry dock Dewey, which passed through the Suez Canal on the way to the Philippine Islands. The size of the locks was determined from the provisions of the Act of Congress approved June 28, 1902, which states: Such canal shall be of sufficient capacity and depth as shall afford convenient passage for vessels of the largest tonnage and greatest draft now in use, and such as may be reasonably anticipated. . . . .'

In considering the limiting dimensions of the locks, and thus of the canal, it must be borne in mind that there has been a steady increase in the size of ships, upon which great emphasis has been laid. If curves are plotted to show the growth in length, width, depth and tonnage, especially if the maximum ship of each period is taken, and if these curves are extended to show future developments, the predictions are alarming. However, when the curves are produced beyond a certain point other factors not hitherto considered, and having no influence on the curves as plotted, are likely to enter. Shipbuilding has undergone an almost untrammelled development; building facilities, capital and cost have seemingly not retarded growth. Harbors have been deepened, channels have been widened, wharves, docks, locks and wet basins. have been increased in size, to make way for the leviathans. The impetus toward larger vessels has undoubtedly been from economic reasons. Shipowners have found that with the larger and better equipped ships, having in view passenger traffic and advertising effects as well as freight, their ratio of income has increased and there has been nothing to curb their efforts. Communities and governments have, in their striving for all-important commercial growths, paid the bills for harbor development. As economic conditions have brought about the steep rise in the shipgrowth curve, so economic conditions, but in another field, will

FIG. 15. Mindi Excavation, view looking north from west bank, showing intersection of French and American canals. Atlantic entrance of canal in distance. March, 1913.

tend to flatten the curve. There must be a limit beyond which harbor development cannot economically go, and beyond which the sum of the cost of shipping and building and the cost of construction and maintenance of port works will increase rather than decrease. It will be difficult to determine when this point is reached, especially because the same interests do not provide capital for both enterprises. There are already occasional indications that this factor is entering. The difficulty in providing for the largest ships in New York harbor, while from one standpoint a physical one, is in the last analysis economic.

There is now no commercial necessity why the Panama Canal should accommodate the largest ships; the largest ships may be regarded as ocean ferries with fixed ports. The total estimated traffic capacity of 80,000,000 tons can be handled in ships under Coo feet long, which comprise 95 per cent of the world's tonnage, but within the next generation the canal may become one of the elements which exercise a retardant influence on the maximum size of ships, depending on developments in the commerce of the world.

More important is the effect of the canal on the size of naval vessels. Battleships of the United States have increased in beam from 76 feet in 1900 (date of authorization) to 80 feet in 1905, 88 feet in 1908, and about 98 feet in 1912; and if this ratio of increase is maintained, the limiting beam would be reached in ships authorized in about 1915.

It is worthy of note that the locks of the enlarged Kaiser Wilhelm Canal from the Baltic to the North Sea are 1082 feet long and 147 feet wide, but the lift is very much less than at Panama.

THE SEA-LEVEL SECTIONS AND THE TERMINALS.

Limon Bay, through which the Atlantic sea-level section passes, faces directly north and is open to the northerly storms and seas, which are quite severe at certain times. Protection was necessary in order, first, that ships might enter the canal in quiet water; second, to provide a quiet anchorage; third, to make traffic in small boats feasible and safe between the shore and ships at anchor; fourth, to prevent the movement of silts and sands by the seas and the attendant dredging expenditure. (See plan No. 2.)

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