STORY OF EXPERIMENTS IN MECHANICAL FLIGHT. 175 



weight, but was only secured after long experiment. It may be added 

 tliat all the aerodromes from the very nature of their construction were 

 wasteful of heat, the industrial efficiency little exceeding half of 1 per 

 cent, or from one-tenth to one-twentieth that of a stationary engine 

 constructed under favorable conditions. This last aerodome lifted 

 nearly 30 per cent of its weight upon the pendulum, which implied that 

 it could lift much more than its weight when running on a horizontal 

 track, and its engines were capable of running its 50-centimeter pro- 

 pellers at something over 700 turns per minute. There was, however, 

 so much that was unsatisfactory about it, that it was deemed best to 

 proceed to another construction before an actual trial was made in the 

 field, and a new aerodrome, designated as In^o. 4, was begun. This last 

 was an attempt, guided by the weary experience of preceding failures, 

 to construct one whose engines should run at a much higher pressure 

 than heretofore, and be much more economical in weight. The experi- 

 ments with the Serpolet boilers having been discontinued, the boiler 

 was made with a continuous helix of copper tubing, which, as first 

 employed, was about three millimeters internal diameter; and it may 

 be here observed that a great deal of time was subsequently lost in 

 attempts to construct a more advantageous form of boiler for the actual 

 purposes than this simple one, which, with a larger coil tube, eventually 

 proved to be the best; so that later constructions have gone back to 

 this earlier tyj^e. A great deal of time was lost in these experiments 

 from my own unfamiliarity with steam engineering, but it may also be 

 said that there was little help either from books or from counsel, for 

 everything was here sui generis, and had to be worked out from the 

 beginning. In the construction which had been reached by the middle 

 of the third year of experiment, and which has not been greatly differed 

 from since, the boiler was composed of a coil of copper in the shape of 

 a hollow helix, through the center of which the blast from the selopile 

 was driven, the steam and water passing into a vessel I called the 

 "separator," whence the steam was led into the engines at a pressure 

 of from 70 to 100 pounds (a pressure which has since been considerably 

 exceeded). 



From the very commencement of this long investigation the great 

 difficulty was in keeping down the weight, for any of the aerodromes 

 could probably have flown had they been built light enough, and in 

 evi^ry case before the construction was completed the weight had so 

 increased beyond the estimate, that the aerodrome was too heavy to 

 fiy, and nothing but the most persistent resolution kept me in continu- 

 ing attempts to reduce it after further reduction seemed impossible. 

 Toward the close of the year (1893) I had, however, finally obtained an 

 aerodrome with mechanical power, as it seemed to me, to fly, and I pro- 

 cured, after much thought as to where this flight should take place, a 

 small house boat, to be moored somewhere in the Potomac; but the 

 vicinity of Washington was out of the question, and no desirable place 



