366 Forbes, Concerning the Flight of Quits. [J^S 



superfluous. In the first of these he says at the outset, -"I 

 premise that it' we know anything about mechanics it is certain 

 that a bird irifhoitt working his wings cannot, either in still air or in a 

 uniform horizontal wind, maintain his level indefinitely." 



This states concisely my main contention. Subsequently he 

 names two possible conditions o( continued soaring in other than a 

 downward direction; v'^ ascending currents and (2) variations in 

 velocity or direction in different portions of the air. In his discus- 

 sion he devotes more attention to the second condition, and cites 



an example of observed flight which seems to exemplify this prin- 

 ciple. 1 scarcely mentioned the possibility of explanation by this 

 latter principle of irregularities in the wind, for though it occurred 

 tome as logically conceivable, it seemed too improbable in the case 

 described by Mr. Brewster to be worth dwelling on. 



The references to Lord Rayleigh's papers are ;is follows: "The 

 Soaring o^i Birds." Nature, Vol. XXVII, p. 534. 1883. (Col- 

 lected Scientific Papers, No. 98, Vol. 11. p. 194.) 



-The Sailing Plight of the Albatross." Nature, XI.. p. 34, 

 L889. (ColLSci. Papers, No. L59. Vol. HI. p. 267.) 



"The Mechanical Principles of Flight." Manchester Memoirs, 

 Vol. XLIV, p. 1. L900. (Coll. Sci. Papers. No. 257, Vol. IV, p. 

 462.) 





