CHAPTER X. 



SUMMARY. 



The essential feature of the present work has been the insistance on the 

 importance of a somewhat unfamiliar idea — that rapid aerial locomotion can be 

 effected by taking advantage of the inertia of the air and its elasticity. Though 

 the fact that the air has inertia is a familiar one, and though the flight of certain 

 missiles has indicated that this inertia may be utilized to support bodies in rapid 

 motion, the importance of the deductions to be made has not been recognized. 

 This work makes the importance of some of these deductions evident by experi- 

 ment, and perhaps for the first time exhibits them in their true import. 



This memoir is essentially a presentation of experiments alone, without 

 hypotheses, and with only such indispensable formulas as are needed to link the 

 observations together. These experiments furnish results which may be suc- 

 cinctly summarized as follows : 



The primary experiment with the Suspended Plane is not intended per se 

 to establish a new fact, but to enforce attention to the neglected consequences of 

 the fundamental principle that the pressure of a fluid is always normal to a 

 surface moving in it, some of these consequences being (1) that the stress neces- 

 sary to sustain a body in the air is less when this is in horizontal motion than 

 when at rest; (2) that this stress instead of increasing, diminishes with the 

 increase of the horizontal velocity (a fact at variance with the conclusions of 

 some physicists of repute and with ideas still popularly held) ; (3) that it is at 

 least probable that in such horizontal flight up to great velocities the greater the 

 speed the less the power required to maintain it, this probability being already 

 indicated by this illustrative experiment, whi!e demonstrative evidence follows 

 later. 



The experiments which are presented in Chapter IV result in an empirical 

 curve, giving the ratio between the pressure on an inclined square plane and 

 on a normal plane moving in the air with the same velocity. Incidentally it 

 is shown that the pressure is normal to the inclined surface, and hence that the 

 effects of skin-friction, viscosity, and the like are negligible in such experiments. 

 It is also shown that for the small angles most used in actual trial of the plane, the 

 pressure on it is about 20 times greater than that assignable from the theoretical 

 formula derived from Newton's discussion of this subject in the Principia. This 



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