to contain marine warning beacons. This project never got under the ground. In 1858, an attempt to assassinate Napoleon III brought France into the Italian war against Austria, and when word spread in France that the assassin's bombs had been made in Birmingham, a chill developed between the French and British Governments. This led to a wave of fear in England that another Napoleon might try a cross-Channel invasion. All this froze out Thomé de Gamond's tunnel-promoting for several years. He did not try again until 1867, when he exhibited a set of revised plans for his Varne tunnel at the Universal Exhibition in Paris. In doing so he concluded that he had pushed the cause of the tunnel about to the limit of his personal powers. Thirty-five years of work devoted to the problem had cost him a moderate personal fortune, and he was obliged to note in presenting his plan that "the work must now be undertaken by collective minds well versed in the physiology of rocks and the workings of subterranean deposits." After that, Thomé de Gamond retired into the background, squeezed out, it may be, by other tunnel promoters. In 1875, an article in the London _Times_ that mentioned his name in passing reported that he was "living in humble circumstances, his daughter supporting him by giving lessons on the piano." He died in the following year. Although Thomé de Gamond's revised plan of 1867 came to nothing in itself, it did cause renewed talk about a Channel tunnel. The new spirit of free trade was favorable to it among Europeans, and everybody was being greatly impressed with reports of the striking progress on various great European engineering projects of the time that promised closer communication between nations—the successful cutting of the Isthmus of Suez, the near completion of the 8.1-mile-long Mount Cenis rail tunnel, and the opening, only a few years previously, of the 9.3-mile-long St. Gotthard Tunnel, for example. Hardly any great natural physical barriers between neighboring nations seemed beyond the ability of the great nineteenth-century engineers to bridge or breach, and to many people it appeared logical enough that the barrier of the Dover Strait should have its place on the engineers' list of conquests. In this generally propitious atmosphere, an Englishman named William Low took up where Thomé de Gamond left off. Shortly after the Universal Exhibition, Low came up with a Channel tunnel scheme based principally upon his own considerable experience as an engineer in charge of coal mines in Wales. Low proposed the creation of a pair of twin tunnels, each containing a single railway track, and interconnected at intervals by short cross-passages. The idea was a technically striking one, for it aimed at making the tunnels, in effect, self-ventilating by making use of the action of a train entering a tunnel to push air in front of it and draw fresh air in behind itself. According to Low's scheme,