NO. 3 l,A\<;l,l',Y MEMOIR ON MECHANICAL IU..IU 11 



There is hut a very partial analogy in this case to the launching of a ship, 

 which is held to her ways by her greal weight. Here, the" ship " is liable to rise 

 from her ways or be turned over laterally at any instant, unless it is securely 

 fastened to them in a manner to prevent its rising, but not to prevent its 

 advancing-. 



The experiments with rubber-driven models commenced in April, 1887, at 

 the Allegheny Observatory, were continued at intervals (partly there, but chiefly 

 in Washington) for three or four years, during which time between thirty and 

 forty independent models were constructed, which were so greatly altered in the 

 course of experiment that more nearly one hundred models were in reality tried. 

 The result of all this extended labor was wholly inconclusive, but as subsequent 

 trials of other motors (such as compressed air, carbonic-acid gas, electric bat- 

 teries, and the like) proved futile, and (before the steam engine) only the rubber 

 gave results, however unsatisfactory, in actual flight, from which anything could 

 be learned, I shall give some brief account of these experiments, which preceded 

 and proved the necessity of using the steam engine, or other like energetic motor, 

 even in experimental models. 



An early attempt was made in April, 1887, with a model consisting of a frame 

 formed of two wooden pieces, each about 1 metre long and 4 centimetres wide, 

 made for lightness, of star-shaped section, braced with cross-pieces and carrying 

 two long strips of rubber, each about 1 mm. thick, 30 mm. wide, 2 metres long, 

 doubled, weighing 300 grammes. Each of these strips could be wound to about 

 300 turns, one end being made fast to the front of the frame, the other to the shaft 

 of a four-bladed propeller 30 cm. in diameter. The wings were made of lightest 

 pine frames, over which paper was stretched, and were double, one being super- 

 posed upon the other. Each was 15 cm. wide, and 120 cm. long. The distance 

 between them was 12 cm. and the total surface a little more than 3600 sq. cm. 

 (4 square feet). In flying, the rubber was so twisted that the propellers were run 

 in opposite directions. The weighi of the whole apparatus was not quite 1 kilo- 

 gramme, or about 1 pound to 2 feet of sustaining surface, which proved to be 

 entirely too great a weight for the power of support. When placed upon the 

 whirling-table, it showed a tendency to soar at a speed of about ten miles an 

 hour, but its own propellers were utterly insufficient to sustain it. 



In this attempt, which was useful only in showing how much was to be learned 

 of practical conditions, the primary difficulty lay in making the model lighl 

 enough and sufficiently strong to support its power. This difficulty continued to 

 be fundamental through every later form .-but besides this, the adjustment of the 

 center of gravity to the center of pressure of the wings, the disposition of the 

 wings themselves, the size of the propellers, the inclination and number of their 

 blades, and a great number of other details, presented themselves for examina- 



