QN AERIAL NAVIGATION. J^l 



the line of its path, at a velocity of about 34 or 35 feet pel- 

 second. 



Let a b, fig. 2, represent such a surface or sail made of Applied to the 



thin cloth, and containing about 200 square feet (if of a the ? ry ° fae «*l 



l v navigation* 



square form the side will be a little more than 14 feet) ; and 



the whole of a firm texture. Let the weight of the man and 

 the machine be 200 pounds. Then if a current of wind 

 blew in the direction c d, with a velocity of 35 feet per se- 

 cond, at the same time that a cord represented by c d would 

 sustain a tension of 21 pounds, the machine would be sus- 

 pended in the air, or at least be within a few ounces of it 

 (falling 1 short of such support only in the ratio of the sine 

 of the angle of 94 degrees compared with radius ; to ba- 

 lance which defect, suppose a little ballast to be thrown out) 

 for the line de represents a force of 200 pounds, which, as 

 before, being resolved into df and fe, the former will re- 

 present the resistance in the direction of the current, and 

 the latter that which sustains the weight of the machine. 

 It is perfectly indifferent whether the wind blow against the 

 plane, or the plane be driven with an equal volacity against 

 the air. Hence, if this machine were pulled along by a 

 cord c d, with a tension of about 21 pounds, at a velocity 

 of 35 feet per second, it would be suspended in a horizontal 

 path; and if in lieu of this cord any other propelling power 

 were generated in this direction, with a like intensity, a si- 

 milar effect would be produced. If therefore the waft of 

 surfaces advantageously moved, by any force generated 

 within the machine, took place to the extent required, aerial 

 navigation would be accomplished. As the acuteness of the 

 angle between the plane and current increases, the propel- 

 ling power required is less and less. The principle is simi- 

 lar to that of the inclined plane, in *hich theoretically on» 

 pound may be made to sustain all but an infinite quantity; 

 for in this case, if the magnitude of the surface be increased 

 ad iniinituiTi, the angle with the current may be diminished, 

 and consequently the propelling force, in the same ratio* 

 In practice, the extra resistance of the car and other parts 

 of the machine, which consume a considerable portion of 

 power, will regulate the limits to which this principle, which 

 is the true basis of aerial navigation, cmt- be carried; and 



the- 



