THE EFFORT TO CONCEAL COMBATANTS.--The French have discarded the historic red trousers, and the elimination of lace, white gloves, and other telltale insignias of the officers, have been dispensed with by special orders. In the great European war armies have burrowed in the earth along battle lines hundreds of miles in length; made covered trenches; prepared artificial groves to conceal batteries, and in many ingenious ways endeavored to make the battlefield an imitation field of nature. SMOKELESS POWDER.--While smokeless powder has been utilized to still further hide a fighting force, it has, in a measure, uncovered itself, as the battlefield is not now, as in olden times, overspread with masses of rolling smoke. Nevertheless, over every battlefield there is a haze which can be penetrated only from above, hence the possibilities of utilizing the aeroplane in war became the most important study with all nations, as soon as flying became an accomplished fact. INVENTIONS TO ATTACK AERIAL CRAFT.--Before any nation had the opportunity to make an actual test on the battlefield, inventors were at work to devise a means whereby an aerial foe could be met. In a measure the aerial gun has been successful, but months of war has shown that the aeroplane is one of the strongest arms of the service in actual warfare. It was assumed prior to the European war that the chief function of the aeroplane would be the dropping of bombs,--that is for service in attacking a foe. Actual practice has not justified this theory. In some places the appearance of the aeroplane has caused terror, but it has been found the great value is its scouting advantages. FUNCTION OF THE AEROPLANE IN WAR.--While bomb throwing may in the future be perfected, it is not at all an easy problem for an aviator to do work which is commensurate with the risk involved. The range is generally too great; the necessity of swift movement in the machine too speedy to assure accuracy, and to attack a foe at haphazard points can never be effectual. Even the slowly-moving gas fields, like the Zeppelin, cannot deliver bombs with any degree of precision or accuracy. BOMB-THROWING TESTS.--It is interesting, however, to understand how an aviator knows where or when to drop the bomb from a swiftly-moving machine. Several things must be taken into consideration, such as the height of the machine from the earth; its speed, and the parabolic curve that the bomb will take on its flight to the earth. When an object is released from a moving machine it will follow the machine from which it is dropped, gradually receding from it, as it descends, so that the machine is actually beyond the place where the bomb strikes the earth, due to the retarding motion of the atmosphere against the missile.