INTRODUCTION. 



15 



fluid, ^.g. yielding media, the propeller itself must yield. Of 

 this I am fully satisfied from observation and experiment. 

 The propellers at present employed in navigation are, in my 

 opinion, faulty both in principle and application. 



The observations and experimxcnts recorded in the present 

 volume date from 1864. In 18671 lectured on the subject of 

 animal mechanics at the Eoyal Institution of Great Britain : ^ 

 in June of the same year (1867) I read a memoir " On the 

 Mechanism of Flight" to the Linnean Society of London 

 and in August of 1870 I communicated a memoir " On the 

 Physiology of Wings" to the Eoyal Society of Edinburgh.^ 

 These memoirs extend to 200 pages quarto, and are illus- 

 trated by 190 original drawings. The conclusions at which 

 I arrived, after a careful study of the movements of walking, 

 swimming, and flying, are briefly set forth in a letter addressed 

 to the French Academy of Sciences in March 1870. This 

 the Academy did me the honour of publishing in April of 

 that year (1870) in the Comptes Eendus, p. 875. In it I 

 claim to have been the first to describe and illustrate the 

 following points, viz. : — 



That quadrupeds walk, and fishes swim, and insects, bats, 

 and birds fly by figure-of-8 movements. 



That the flipper of the sea bear, the swimming wing of the 

 penguin, and the wing of the insect, bat, and bird, are screws 

 structurally, and resemble the blade of an ordinary screw- 

 propeller. 



That those organs are screws fundionoMy, from their twist- 

 ing and untwisting, and from their rotating in the direction 

 of their length, when they are made to oscillate. 



That they have a reciprocating action, and reverse their 

 planes more or less completely at every stroke. 



That the wing describes a figure-of-^ track in space when 

 the flying animal is artificially fixed. 



That the wing, when the flying animal is progressing at 



1 On the various modes of Flight in relation to Aeronautics." — Proceed- 

 ings of the Eoyal Institution of Great Britain, March 22, 1867. 



* ''On the Mechanical Appliances by which Flight is attained in the 

 Animal Kingdom." — Transactions of the Linnean Society, vol. xxvi. 



3 " On the Physiology of Wings." — Transactions of the Eoyal Society of 

 Edinburgh, vol. xxvi. 



