FIG. 16.-Operation of Gatun Locks. Panama R. R. Steamer Allianca has been raised from Atlantic sea level and is entering Gatun Lake from upper west lock chamber. Note adjoining twin lock is empty. Steel structure on left is an emergency dam.

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 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 was probably one of the most perfect ever devised for handling concrete. The cost of the concrete in place was $4.68 per cubic yard in 1911 and $4.77 in 1912.

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 state: "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 ship-growth curve, so economic conditions, but in another field, will 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 600 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.

Before leaving the subject of the locks as the limiting features, it is important to note that no physical obstacle will prevent the engineer of the coming generation from building an additional series of locks, should experience show wider or longer locks to be a real necessity. The cost will be great but not prohibitive and will be but a small fraction of the original