Camouflage, it should be kept in mind, is of two kinds—negative and positive. Negative camouflage consists in the concealment of troops, trenches, mine-shafts, battery positions, ammunition-dumps, hangars, or other objects, knowledge of whose location must be kept, if possible, from the enemy. Positive camouflage, on the contrary, consists in the imitation or suggestion of troops, trenches, batteries, etc., in certain locations, when, in reality, there is nothing of the sort there, in order to deceive and bewilder the enemy. It occasionally became necessary, for example, to convince the Germans that a large troop movement was in progress behind a certain sector of the front, whereas the real movement was taking place scores of miles away. If it was desired to suggest a movement by rail, smoke-pots with clouds of dense black smoke bellying from them were placed on flat cars and moved about from point to point on the military railways. German aviators, observing these columns of smoke at numerous points along the railways, naturally assumed that they came from locomotives hauling troop-laden trains and promptly reported that large bodies of troops were apparently being moved by rail behind the American lines. Thereupon the German commander would rush up his reserves to resist the attack which he believed to be impending. Or, if it was desired to imitate a troop movement by road, the camouflage officer would requisition large numbers of Fords, which would be driven madly along the roads, dragging bundles of brush behind them. The great clouds of dust which thus suddenly appeared on the highways naturally suggested to the German observers that the _verdamte_ Yankees were rushing large bodies of troops to the front by bus or motor-truck. Fooling Fritz was an amusing game while it lasted. This latter ruse, I might mention parenthetically, was not original with the Americans, for President Diaz, of Mexico, once related to me how, when he and his little band of patriots were being hotly pursued by the French forces sent to Mexico to keep Maximilian on his unstable throne, he ordered his vaqueros to cut bundles of mesquite and drag them behind them by their lariats. It was in the dry season, and the dense clouds of yellow dust thus stirred up convinced the French commander that the Mexican force was far stronger than it really was. He thereupon precipitately abandoned the pursuit and a few weeks later General Diaz, having gained the breathing-spell necessary to augment his forces, fought and won the decisive battle of Puebla.