SCIENCE AND INVENTION 239 



dence that in 1900 Langley renewed his study of the 

 flight of soaring birds, the area of their extended 

 wing surface in relation to weight, and the vertical 

 distance between the center of pressure and the cen- 

 ter of gravity in gulls and different species of buz- 

 zards. He noted among other things that the tilting 

 of a wing was sufficient to bring about a complete 

 change of direction. 



By the summer of 1903 two new machines were 

 ready for field trials, which were undertaken from a 

 large house-boat, especially constructed for the pur- 

 pose and then moored in the mid-stream of the 

 Potomac about forty miles below Washington. The 

 larger of these two machines weighed seven hundred 

 and five pounds and was designed to carry an en- 

 gineer to control the motor and direct the flight. 

 The motive power was supplied by the light and 

 powerful gasoline engine already referred to. The 

 smaller aeroplane was a quarter-size model of the 

 larger one. It weighed fifty-eight pounds, had an en- 

 gine of between two and a half and three horse-power, 

 and a sustaining surface of sixty-six square feet. 



This smaller machine was tested August 8, 1903, 

 the same launching apparatus being employed as 

 with the steam-driven models of 1896. In spite of 

 the fact that one of the mechanics failed to withdraw 

 a certain pin at the moment of launching, and that 

 some breakage of the apparatus consequently oc- 

 curred, the aeroplane made a good start, and fulfilled 

 the main purpose of the test by maintaining a per- 

 fect equilibrium. After moving about three hundred 

 and fifty feet in a straight course it wheeled a quar- 

 ter-circle to the right, at the same time descending 



