408 BELL 



far been found impracticable to impart to this frail structure a 

 velocity sufficient to enable it to make headway against any- 

 thing but the mildest sort of wind. The character of the bal- 

 loon problem has therefore changed. Velocity of propulsion 

 rather than dirigibility is now the chief object of research. l 



It has long been recognized by a growing school of thinkers, 

 that an aerial vehicle, in order to cope with the wind, should be 

 specifically heavier than the air through which it moves. This 

 position is supported by the fact that all of Nature's flying 

 models, from the smallest insect to the largest bird, are speci- 

 fically heavier than the air in which they fly, most of them 

 many hundreds of times heavier, and that none of them adopts 

 the balloon principle in flight. It is also significant in this con- 

 nection that some of Santos Dumont's most celebrated exploits 

 were accomplished with quite a small balloon so ballasted as to 

 sink in the air instead of rise. He was then enabled, under the 

 influence of his motive power, to steer his balloon upwards with- 

 out the expenditure of ballast, and to descend without the loss 

 of gas. This probably typifies — for the balloon — the direc- 

 tion of change in the future. A reduction in the volume of gas, 

 coincidently with an increase in motive power, will lead to 

 greater velocity of propulsion — now the main desideratum. 

 Then, dependence upon velocity for support rather than gas, 

 may gradually lead to the elimination of the gas-bag altogether : 

 in which case the balloon will give birth to a flying machine of 

 the heavier-than-air type. 



However this may be it is certainly the case that the tendency 

 of aerial research is to-day reverting more and more to the old 

 lines of investigation that were pursued for hundreds of years 

 before the invention of the balloon diverted attention from the 

 subject. The old devices have been reinvented. The old ex- 

 periments have been tried once more. Again the birds are rec- 

 ognized as the true models of flight ; and again men have put 

 on wings — but this time with more promise of success. 



Lilienthal boldly launched himself into the air in an apparatus 

 of his own construction having wings like a bird and a tail for a 

 rudder. Without any motor he ran down hill against the wind. 



1 Some of the latest forms of dirigible balloon are shown in Plates XIX and XX. 



