THE LANGLEY AERODROME. 207 



titeaui enough, and this was a most wearying one. There must be also 

 a certain amount of wing surface, and large wings weighed prohibit- 

 ively; there must be a frame to hold all together, and the frame, if 

 made strong enough, must yet weigh so little that it seemed impossi- 

 ble to make it. These were the difficulties that I still found myself in 

 after two years of experiment, and it seemed at this stage again as if 

 it must, after all, be given up as a hopeless task, for somehow the 

 thing had to be built stronger and lighter yet. 



Now, in all ordinarj' construction, as in building a steamboaf or a 

 house, engineers have what they call a factor of safety. An iron 

 column, for instance, will be made strong enough to hold live or ten 

 times the weight that is ever going to be put upon it, but if we try 

 anything of the kind here the construction will be too heavy to fly. 

 Everything in the work has got to be so light as to be on the edge of 

 breaking down and disaster, and when the breakdown comes all we 

 can do is to find what is the weakest part and make that part stronger; 

 and in this way work went on, week by week and month by month, 

 constantly altering the form of construction so as to strengthen the 

 weakest parts, until, to abridge a story which extended over years, it 

 was finally brought nearly to the shape it is now, where the completed 

 mechanism, furnishing over a horsepower, weighs collectivel}^ some- 

 thing less than 7 pounds. This does not include water, the amount of 

 which depends on how long we are to run-; but the whole thing, as now 

 constructed, boiler, tire grate, and all that is required to turn out an 

 actual horsepower and more, weighs something less than one one-hun- 

 dredth part of what the horse himself does. I am here anticipating; 

 but after these first three years something not greatly inferior to this 

 was already reached, and so long ago as that, there had accordingly 

 been secured mechanical power to flv, if that were all — but it is not 

 all. 



After that came years more of delay arising from other causes, and 

 I can hardly repeat the long story of subsequent disappointment, 

 which connuenced with the first attempts at actual flight. 



Mechanical power to fly was, as I say, obtained three years ago; the 

 machine could lift itself if it ran along a railroad track, and it might 

 seem as though, when it could lift itself, the problem was solved. I 

 knew that it was far from solved, but felt that the point was reached 

 where an attempt at actual free flight should be made, though the 

 anticipated difficulties of this were of quite another order than those 

 experienced in shop construction. It is enough to look up at the 

 gulls or buzzards soaring overhead, and to watch the incessant rock- 

 ing and balancing which accompanies their gliding motion, to appre- 

 hend that they find something more than mere strength of wing neces- 

 sary, and that the machine would have need of something more than 

 mechanical power, though what this something was was not clear. It 

 looked as though it might need a power like instinctive adaptation to 



