Imagine him for a moment sitting in consultation. His military advisers tell him that the decisive moment has come. "I think, gentlemen," says the minister, turning to his colleagues, "that we are all agreed—the Tunnel must be immediately destroyed. Fire the mine!" "There is one other point," says the officer, "on which I request instructions—at what time am I to execute the order?" "At once, sir; telegraph at once, and in five minutes the blasting charge can be fired." "But," persists the officer, "trains laden with non-combatants are at this moment in the Tunnel. They enter continuously at twenty minutes' intervals; there are never less than four trains, two each way, in the Tunnel at the same time; each train contains some three hundred persons ... I could not destroy twelve hundred non-combatants without very special instructions." And Lord Bury asked, "What would any minister, under such circumstances, do?" As for the proposed defensive measure of flooding the tunnel in case of invasion, General Sir Lintorn Simmons, writing in the same issue of _The Nineteenth Century_, considered it to be a dubious one at best, since, he observed, "it is not to be believed that a great country like France, with the engineering talent she possesses, could not find the means" of pumping all the flood waters out again. An assertion by Dr. Siemens, the electric-lighting expert, that the tunnel could easily be rendered unusable to invaders if its British defenders would pump carbonic-acid gas into it to asphyxiate the intruders, was similarly challenged, in the correspondence columns of the _Times_, by a scientific colleague of his, Dr. John Tyndall. Dr. Tyndall offered to wager Dr. Siemens that the latter could in six hours devise countermeasures that would enable troops to pass unscathed through the tunnel, gas or no gas. Dr. Tyndall illustrated his point by describing an experiment he said he had made on the very day of his letter, while coming down home from London by train, on a part of the South-Eastern line where the speed was thirty miles an hour: I took out my watch and determined how long I could hold my breath without inhalation. By emptying my lungs very thoroughly, and then charging them very fully, I brought the time up to nearly a minute and a half. In this interval I might have been urged through more than half a mile of carbonic-acid gas with no injury and with little inconvenience to myself. Dr. Tyndall concluded, firmly, "The problem of supplying fresh air to persons surrounded by an irrespirable atmosphere has been already solved by Mr. Fleuss and others."