56 L. HAEGEAVE. 



of water is a close analogy to the soaring vortex. The water 

 clearly makes the ball weigh less than nothing. There is little 

 doubt that the weight of a ball dancing on a fountain is greater 

 than when it is at rest. 



The makers of soaring models will find great difficulty in per- 

 suading them to remain tolerably stable in a fore and aft direction. 

 The trouble will be greatly reduced if they avail themselves of 

 the experience of a tight-rope walker with his balancing pole. 

 The acrobat makes his pole as long and stiff as possible, and puts 

 as much weight on the ends of it as he conveniently can, he then 

 has no further difficulty with his athwartships stability. It is 

 the inertia of the weighted ends that takes the wobble out of his 

 body. Likewise the weighted ends of the fore and aft tubular 

 rod in Figs. 1 and 2 check the erratic motion of the vulcanite 

 propeller. 



When you consider the conformation of a soaring bird, it will 

 be noticed that a large part of the under surface is not adapted 

 for the formation of the soaring vortex. The tips of the rigid 

 wings and tail are obviously of such a nature that they will not 

 readily allow the bird to rise or fall suddenly when the soaring 

 parts of the wings are struck by a gust from underneath or above. 

 These surfaces are represented in Figs. 1 and 2 by the horizontal 

 projection of the surfaces of the two cylindrical cells at the ends 

 of the tubular rod. The vertical projection of the two cells repre- 

 sents the vertical surface of a cellular kite or the dihedral angle 

 of some soaring birds. 



The parts of a soaring bird's wings next to the body are repre- 

 sented in Figs. 1 and 2 by the bent sheet of vulcanite. This is 

 the propeller, and it makes sufficient thrust to overcome its own 

 head resistance and that of the rod and two end cells. No attempt 

 has yet been made to ring the changes on the numberless curves 

 that probably soar; the essential points seem to be that the front 

 part of the propeller shall be bent to about the quadrant of a 

 circle, the extreme after part plane, and the intermediate portion 

 hyperbolic. Rigidity of construction is all-important. Springy 



