The United States having decided to take over the responsibility for a task of such advantage to the world's civilisation, gave to it at the outset the benefit of a scientific consideration touched with imagination. There were hills to be levelled, ditches to be dug, water-courses to be tamed, locks to be built. All that was clear enough. But how to secure the safety of the workers? Nature's defenders, though fed fat with victory, were still eager, relentless for new victims. Science said that to build a canal wholesome working conditions must be created: yellow fever and malaria abolished. Science also told how. The massacre of the mosquitoes of the isthmus was the first task in canal-building. The mosquitoes, the disseminators of the deadly tropical diseases, were attacked in their breeding grounds, and their larvæ easily destroyed by putting a film of oil over the surface of the shallow waters in which they lived. The oil smothered the life in the larvæ, and they perished before they had fully developed. The insect fortunately has no great range of flight. Its life is short, and it cannot pass far from its birthplace. Herodotus tells how Egyptians avoided mosquitoes by sleeping in high towers. The natives of Papua escape them by building their huts in the forks of great trees. If the mosquitoes are effectively exterminated within a certain area, there is certainty of future immunity from them within that area if the marshes, the pools--the stagnant waters generally on its boundaries--are thereafter guarded during the hatching season against the chance of mosquito larvæ coming to winged life. At Suez scientists had found this all out. Science conquered the mosquito in Panama as it had been conquered elsewhere, and the entrenchments of Nature crumbled away. Henceforth it was a matter of rock-cutters, steam shovels and explosives, the A B C of modern knowledge. But the mosquito put up a stubborn fight. Driven out of the marshes, it found a refuge in the cisterns of houses, even in the holy-water founts of churches. Every bit of stagnant water within the isthmus area had to be protected against the chance of mosquitoes coming to life before the campaign was successful. To-day the isthmus of Panama is by no means unhealthy, and the work of canal-cutting progresses so well that Mr President Taft was able to announce recently the probability of it being opened two years before the due date. That brings the canal as a realised fact right into the present. Some few facts regarding this engineering work. It will cost about £70,000,000. The total length of the canal to be made from sea to sea is 50-1/2 miles, with a maximum width on the bottom of 1000 feet. The land excavation is 40-1/2 miles of cutting through rock, sand and clay, leaving 10 miles of channel to be deepened to reach the sea at either end. Some of the other construction dimensions are these:--