mirror, which is much more easily manufactured, is far less fragile, costs only a third as much, and possesses almost as great reflecting qualities as the glass ones. The search-light used by the American forces for antiaircraft work is the heavy 60-inch seacoast type—the largest light known—lightened and modified for use in the field, with a range of practically 30,000 feet. As the result of recent experiments it has been found that the visibility at 12,000 feet was 85 per cent, while at 15,000 feet, or nearly 3 miles, it was 43 per cent. In order to obtain these standards of comparison for visibility for search-lights, an aviator was directed to fly back and forth through the beam a certain number of times. If the observers on the ground recorded the full number of passages across the beam, 100 per cent was registered, this occurring regularly at 5,000 feet, and in most cases during tests at 8,000 feet. The percentage of visibility was, in other words, the number of times the airplane was seen to the number of times it crossed the beam. * * * * * When warfare of movement becomes stabilized into position or trench warfare, it is almost certain that, sooner or later, one side or the other will resort to some form of underground attack. To permit of this subterranean warfare, certain conditions are requisite: the lines must be fairly close together, the level of the ground-water must be deep, and the ground itself must not be too hard. These obstacles to successful mining are not insuperable, however, for, preparatory to their assault on Messines Ridge, the British drove a tunnel which was a mile in length, and on the Carso I saw Italian engineers driving their galleries through solid rock. France and England early recognized the importance of this form of warfare and organized their miners accordingly, and, upon our entrance into the war, we too organized and sent to France a mining regiment—the 27th Engineers. It is estimated that by the summer of 1918 there were upward of 40,000 skilled miners on the Western Front, these soldiers of the pick and drill having been brought from the remotest corners of the earth—from the Yukon, the Rand, and the Congo, from Mexico, Australia, and California. In my “Vive la France!” I told, if I remember rightly, of the Cornish miners, known as “kickers,” who lay on their backs, as they do in the tin mines in Cornwall, where the galleries are so low that there is no room to swing a pick, and kicked away the earth by means of a sort of spur attached to their heels.