174 Transact io7is. — MisceltaneoKS. 



piece of thin, stiff card- board and cut a cross out of it ; a slight obliquity is 

 th'en imparted to the arms or planes, and a piece of wood is cemented 

 through the centre to act as a vertical axis ; if, then, rotation be imparted 

 to it by the finger and thumb, it readily rises to the ceUing of the room. 

 Varying the experiments as regards shape, etc., it is found advantageous to 

 construct the planes broader towards the cu-cumfereuce ; secondly, to bend 

 the broad ends or tips somewhat downwards ; and, thirdly, to impart a 

 slight screw-form to the vanes in imitation of that possessed by a feather. 



The boomerang, used as a missile by the Austrahan natives, affords an 

 examxDle how a horizontal force can be transformed into a lifting force. 

 The wheel, here exhibited, has been devised with the idea of securing the 

 planes in theii- true position, especially towards the tips, and of discarding 

 all dead weight in those parts near the centre of the wheel where the motion 

 of rotation is too slow to assist in elevating it. To effect these, I have 

 constructed a horizontal wheel in which the cu'cumfereuce is, as it were, 

 the basis or skeleton, and the radii act by tension so as to retam a hght 

 vertical axis iu the centre. In this manner a surprisingly large, strong, 

 and light wheel is obtained, the necessary weight of the circumference 

 being utihzed, as will afterwards be explained. 



Two systems of radii are attached to the circumference of the wheel, 

 each system containing eight pairs of tension strings ; the tension of all 

 these radii can be thus increased simultaneously by simply widening the 

 systems on the axis. 



By an inspection of the model, it will be seen that narrow pieces of 

 tracing-cloth are attached between each paii' of the tension strings ; the 

 anterior edge of each plane is attached to the upper side of the cu'cum- 

 ference, and the posterior edge to the lower side of it. The thickness of 

 the rim thus gives the degree of obliquity of the planes, namely, 5° at the 

 tips, while the planes are nearly horizontal near the axis. By this 

 arrangement the resistance of the air to the motion of the radii is utilized 

 in buoying up the wheel ; and as the axis can be turned dh-ectly by a crank, 

 the necessary speed of the cu'cumference can be obtained by simply making 

 the wheel large enough, thus dispensing with the friction which would arise 

 if multiplying wheels were used — size of the wheel forming no theoretical 

 objection in the Hmitless expanse. The waste of power by resistance and 

 friction can be thus reduced to a minimum. 



Though there must be great difficulty in observing the shape and position 

 which the individual feathers and mngs of birds assume while in actual 

 flight, yet it is easy to fix them in a current of air and so watch the effect. 

 In this way it will be seen that the posterior and thin edge of the feather 

 yields more than the other parts in flight, especially towards the tips. The 



