One of the very first heavier-than-air flights ever recorded is said to have been made by a Japanese who dropped bombs from an immense man-carrying kite during the Satsuma rebellion of 1869. The kite as a flying machine has, however, two drawbacks: it needs the wind--it cannot fly in a calm--and it stands still. One early effort to improve on this situation was made in 1856, when a man was towed in a sort of kite which was hauled by a vehicle moving on the ground. In February of the present year, Lieut. John Rodgers, U.S.N., was lifted 400 feet from the deck of the cruiser _Pennsylvania_ by a train of eleven large kites, the vessel steaming at twelve knots against an eight-knot breeze. The aviator made observations and took photographs for about fifteen minutes, while suspended from a tail cable about 100 feet astern. In the absence of a sufficient natural breeze, an artificial wind was thus produced by the motion imparted to the kite; and the device permitted of reaching some destination. The next step was obviously to get rid of the tractive vehicle and tow rope by carrying propelling machinery on the kite. This had been accomplished by Langley in 1896, who flew a thirty-pound model nearly a mile, using a steam engine for power. The gasoline engine, first employed by Santos-Dumont (in a dirigible balloon) in 1901, has made possible the present day _aeroplane_. [Illustration: SUSTAINING FORCE IN THE AEROPLANE] What "keeps it up", in the case of this device, is likewise its velocity. Looking from the side, _ab_ is the sail of the aeroplane, which is moving toward the right at such speed as to produce the equivalent of an air velocity _V_ to the left. This velocity causes the direct pressure _P_, equivalent to a lifting force _L_ and a retarding force _R_. The latter is the force which must be overcome by the motor: the former must suffice to overcome the whole weight of the apparatus. Travel in an aeroplane is like skating rapidly over very thin ice: the air literally "doesn't have time to get away from underneath." [Illustration: DIRECT, LIFTING, AND RESISTING FORCES If the pressure is 10 lbs. when the wind blows directly toward the surface (at an angle of 90 degrees), then the forces for other angles of direction are as shown on the diagram. The _amounts_ of all forces depend upon the wind velocity: that assumed in drawing the diagram was about 55 miles per hour. But the _relations_ of the forces are the same for the various angles, no matter what the velocity.]