422 Transactions of the South African Philosophical Society. 



effort, over the vessel going at high speed. The diagram shows how 

 the wind is deflected upwards by the ship's side. 



Land birds take advantage of upward currents also. I observed 

 a hawk rise to a height of some three thousand feet, ascending in a 

 spiral without a single flap of its wings. On another occasion I saw 

 a hawk beating a paddock suddenly commence to ascend in spirals. 

 While watching the marvellous performance the dust rose in a 

 whirlwind from an adjacent road, rendering visible the tourbillon of 

 which the bird was taking advantage to get upward. I have seen a 



number of vultures poised, stationary as a boy's kite, over the slope 

 of a hill, evidently, utilising the upward slant of the wind produced 

 by the liill. Vultures utilise their own inertia to mount. 



^ Direction of Wind. 



SIDE ELEVATION OF BIRD's TRACK IN AIR. 



PLAN OP P.IRD S TRACK. 



