The belief in concrete among the builders of the Panama Canal has been almost a superstition. They invented a sort of cement gun to shoot sand and water against the sides of the Culebra Cut, so as to form a coating of solid artificial rock, but the experiment rather deserved than achieved success. Of course all such structures as lighthouses were built wholly of concrete, and it is reported that even barges were constructed of this adaptable material. As regards concrete and its nature and behaviour nothing was taken for granted. Every means was taken of testing such important matters as the effect of sea-water on this material, the time it takes for these huge masses of artificial stone to settle, and many other questions on the answer to which the permanence and stability of the locks and the entire waterway would depend. The Panama Canal, writes Mr. Showalter, is "the greatest effort man ever has made, and perhaps ever will make, to simulate the processes of geologic ages, and do in days what Nature required unreckoned years to accomplish." These remarks about concrete naturally lead us to the subject of the Panama locks, the magnificent stairway at Gatun, the single-step locks at Pedro Miguel (or, as the worker quickly Anglicized it, Peter Magill), and the double-step flight at Miraflores. The most impressive of these is the colossal duplicated three-step flight at Gatun, up which the vessel in transit is lifted from the end of the sea-level seven-mile-long entrance channel through Limon Bay to Gatun up to the surface of Gatun Lake, 85 feet above the level of the sea. This giant staircase has been constructed in a cutting through the hill which retains at this end the waters of the artificial lake. A tremendous amount of excavation, upwards of 5,000,000 cubic yards, was necessary, and the locks, which are constructed entirely of concrete, contain about 2,046,100 cubic yards of that material. The chambers of all the locks in the canal will have a usable length of 1,000 feet and a width of 110 feet. These dimensions should prove large enough for the largest ships not only existing but likely to be constructed for many years to come. They satisfy the requirement of the Spooner Act that the canal shall be "of sufficient capacity and depth to afford convenient passage for vessels of the largest tonnage and greatest draft now in use, and such as may reasonably be expected." More than 95 per cent. of the ships now afloat are less than 600 feet in length, so that a good margin is allowed. We may be certain that the American government has given the closest attention to the question of the length and breadth of the lock-chambers, for the canal, we must remember, is primarily a military passage for the purpose of transferring, if need be, the entire American fleet from the Atlantic to the Pacific seaboard. The locks of the Kiel Canal, it may be added for purposes of comparison, have an available length of 492 feet and a width of 82 feet.