x PRACTICAL PURPOSE 287 



be sustained in the air if made to advance through it 

 fast enough. 



Until a few years ago, very little was known of the 

 resistance offered to air by a body advancing through it. 

 Sir Isaac Newton considered the subject, and came to 

 the conclusion that the resistance opposed to a thing 

 in rapid motion would be so great that enormous 

 mechanical power would be required if artificial flight 

 were to be accomplished. It was not a practical 

 engineer or an aviator who undertook experiments to 

 test the rule which Newton gave to calculate this power, 

 but an American man of science Samuel Pierpont 

 Langley, secretary of the Smithsonian Institution of 

 Washington. 



Prof. Langley commenced his experiments in 1887 ; 

 and his work gave, for the first time, some accurate 

 knowledge as to the resistance offered to planes moving 

 through air at different speeds and inclinations. He 

 proved that what had been called the Newtonian Law 

 was wrong ; and that it takes less power to support a 

 plane moving through air at high speed than at low. 

 By simply moving a given weight fast enough in a hori- 

 zontal plane, Langley found that it was possible to 

 sustain the weight with less than one-twentieth the power 

 demanded by Newton's rule. His conclusion as to the 

 relation of speed to power for a body in motion in air 

 was as follows : 



These new experiments (and theory also when viewed in their 

 light) show that if in such aerial motion there be given a plane 

 of fixed size and weight inclined at such an angle and moved 

 forward at such a speed that it shall be sustained in horizontal 

 flight, then the more rapid the motion is, the less will be the 

 power required to support and advance it. Prof. S. P. Langley. 



This rule, now known as Langley's Law, represented 



