The most prominent exponent of the tetrahedral type--that made up of numbers of small cells set one upon another--is the _Cygnet_ of Dr. Alexander Graham Bell, which perhaps is more a kite than a true flying machine. The first _Cygnet_ had 3,000 cells, and lifted its pilot to a height of 176 feet. The _Cygnet II_. has 5,000 tetrahedral cells, and is propelled by a 50 horse-power motor. It has yet to make its record. One of the most recently devised machines is that known as the Fritz Russ flyer. It has two wings, each in the form of half a cylinder, the convex curve upward. It is driven by two immense helical screws, or spirals, set within the semi-cylinders. No details of its performances are obtainable. Chapter VIII. FLYING MACHINES: HOW TO OPERATE. Instinctive balance--When the motor skips--Progressive experience--Plum Island School methods--Lilienthal’s conclusions--The Curtiss mechanism and controls--Speed records--Cross-country flying--Landing--Essential qualifications--Ground practice--Future relief. Any one who has learned to ride a bicycle will recall the great difficulty at first experienced to preserve equilibrium. But once the knack was gained, how simple the matter seemed! Balancing became a second nature, which came into play instinctively, without conscious thought or effort. On smooth roads it was not even necessary to grasp the handle-bars. The swaying of the body was sufficient to guide the machine in the desired direction. Much of this experience is paralleled by that of the would-be aviator. First, he must acquire the art of balancing himself and his machine in the air without conscious effort. Unfortunately, this is even harder than in the case of the bicycle. The cases would be more nearly alike if the road beneath and ahead of the bicyclist were heaving and falling as in an earthquake, with no light to guide him; for the air currents on which the aviator must ride are in constant and irregular motion, and are as wholly invisible to him as would be the road at night to the rider of the wheel. And there are other things to distract the attention of the pilot of an aeroplane--notably the roar of the propeller, and the rush of wind in his face, comparable only to the ceaseless and breath-taking force of the hurricane.