THE COMPONENT PRESSURE RECORDER. 67 



weight multiplied by V tan a, the latter factor being the height H to which the 

 plane is virtually lifted against gravity. 



It will be seen, now, that this expression is the same as that derived for the 

 former case, V being the horizontal forward velocity, and a the inclination of the 

 plane to the horizon. In order to prove the perfect identity of significance of 

 the two expressions it, would, however, remain to show experimentally that the 

 relation of T'to a in this new case is the same as that experimentally derived for 

 the first case. I have made no experiments with which to determine this relation, 

 but I may say that, since all the circumstances of the resulting motion seem the 

 same in the one case as in the other, the relation between V and a is presumably 

 the same, and consequently the amount of work done in the second case is 

 presumably the same as that done in the first case ; it is certainly so nearly so 

 that whenever a is small (and it always is so in such economic or horizontal flight), 

 we may, for all practical purposes, assume an identity of the two cases. It fol- 

 lows that, in soaring with (horizontal) velocity V, the direction of propulsion can 

 vary between 0° and a° at will, without sensibly changing the amount of work 

 that is expended, so long as the plane remains at the angle a with the horizon. 



The reader who has followed the description of this instrument will see that 

 the experiments have consisted in measuring with a dynamometer the actual 

 resistance to motion experienced by planes when just "soaring" or supporting 

 themselves under all the circumstances of flight in free air, except that the plane 

 is restricted from the " flouncing " caused by irregular currents, etc., and made 

 to hold a steady flight. 



The most important conclusion may be said to be the confirmation of the 

 statement that to maintain such planes in horizontal flight at high speeds, less power 

 is needed than for low ones. 



In this connection I may state the fact, surely of exti-eme interest in its 

 bearing on the possibility of mechanical flight, that while an engine developing 

 one horse-power can, as has been shown, transport over 200 pounds at the rate 

 of 20 meters per second (-15 miles an hour), such an engine (/. e., engine and 

 boiler) can be actually built to weigh less than one-tenth of this amount. 



