APPLICATIONS TO MECHANICS 89 



steel needle run through the longitudinal fold. This 

 little flying apparatus was allowed to fall in a vertical 

 direction, and its chronophotographic trajectory taken 

 by a series of exposures at intervals of ^o of a second. 

 Fig. 59 shows a reverse tracing of this trajectory, and 

 must be read from the right-hand top corner down- 

 wards and towards the left. 



This object falls at first vertically, with an accele- 

 rated velocity ; but it is soon influenced by the 

 rudder-like action of the curved portion behind, and 

 swinging round advances in a horizontal direction, 

 then by degrees it assumes an upward tendency. At 



£& 



v 



Fig. 59.— Chronophotographic trajectory of a flying apparatus describing a sinuous 

 curve in the air (20 imag ,s to the second). 



this moment the speed decreases, its axis rights itself, 

 and becomes set in almost a vertical position. Next 

 the axis approaches to a horizontal direction, the card 

 takes a new plunge with the apex directed downwards, 

 and is about to turn upside down in a new phase of 

 accelerated velocity, only at this moment the experi- 

 ment comes to a sudden termination. 



All these extraordinary evolutions, which nowadays 

 are perfectly familiar to "aviators," after long and 

 patient researches, are explained by them as following 

 the laws of Avanzini and Joessel, who showed that if a 

 thin lamina of any substance were obliquely propelled 



