Miscellaneous. 217 



liis experiments he concludes that the wing moves from behind for- 

 wards both ill its descent and in its ascent. 



That the plane of the wing changes twice during each movement 

 appears from the difference in the brilliancy of the two branches of 

 the luminous figure of 8. When a branch is very brilliant, this is 

 because it presents its gilt surface at a favourable angle for the re- 

 flection of the sun's light. During descent the wing presents its 

 upper surface a little forward, whilst during elevation this surface 

 looks rather backward. 



These movements are so complex that they would require a very 

 complex muscular apparatus if each of them was the result of a 

 special act. It would require a very perfect coordination to enable 

 these eight or ten successive actions to be reproduced in regular order 

 at each revolution of the wing — that is to say, from two hundred to 

 three hundred times in a second ; but the simple elevation and de- 

 pression of the wing is sufficient to enable the resistance of the air 

 to produce all the other movements. The wing being rigid in front, 

 in consequence of its thick nervures, the flexible hinder part, being 

 raised by the resistance of the air during the rapid depression of the 

 wing, will acquire an oblique direction, so that the upper surface of 

 the wing will look forward ; on the other hand, during elevation 

 the resistance of the air will be above, and the upper surface of the 

 wing will incline backwards. This figure-of-8 movement exactly 

 resembles the motion of the oar in sculling a boat. 



To verify his theory, the author has constructed a small apparatus, 

 which he describes as follows : — A mechanism set in motion by an 

 air-pump caused the alternate elevation and depression of a pair of 

 wings constructed on the plan of those of insects. This apparatus 

 had not sufficient motive power to raise its own weight ; but it was 

 placed upon a pivoted rod in equilibrium, so that, if the apparatus de- 

 veloped the motive power required by the theory, the whole would 

 acquire a movement of rotation round a central axis. On being set in 

 action, the apparatus rotated rapidly. 



By gilding the tip of one of the wings of this artificial insect, all 

 the movements and changes of plane executed in the flight of an in- 

 sect were reproduced by the apparatus ; and as the force derived 

 from the pump can only produce elevations and depressions of the 

 wing in the same plane, it is evident that the other movements are 

 produced by the resistance of the air. 



The origin of this theory of flight is to be found in Borelli, who 

 supposes that the wing of a bird acts upon the air in the manner of 

 a wedge. Strauss-Durckheim states this opinion more clearly, and 

 shows how the insect derives, from the resistance of the air to the 

 inclined plane of its wing, a combination which it employs to sustain 

 and guide itself. Girard has made experiments to show the correct- 

 ness of Strauss-Durckheim's hypothesis, and proved that if the flexi- 

 bility of the hinder margin of the wing be altered by a dry coating 

 of any kind, the power of flight is destroyed. — Comptes Rendus, 

 March 15, 1869, tome Ixviii. pp. 667-669. 



