334 DE PETTIGEEW ON THE PHYSIOLOGY OF WINGS. 



figure of 8. Whether this figure be more or less apparent, whether its branches 

 be more or less equal, matters little ; it exists, and an attentive examination will 

 not fail to reveal it."""" 



Professor Marey's experiments, I may add, have been repeated and verified 

 in England by Mr Senecal. This investigator also represents and describes the 

 double loop and figure of 8 movements.^ These two sets of experiments con- 

 ducted independently, and after a considerable interval, by M. Marey and Mr 

 Senecal respectively, will, I hope, suffice to establish the absolute correctness 

 of the " Figure of 8 or Wave theory of Flight." 



NATURAL FLIGHT.} 



Method of Testing the Accuracy of the Figure of 8 Theory of Wing Move- 

 ments. — The correctness of the figure of 8 theory of flying may be readily estab- 

 lished by a careful study of the rapidly vibrating wing of the wasp or common 

 blow-fly. 



If the body of the former be held, and the wing made to vibrate in front of 

 a dark screen, it will be found that not only the tip but also the margins of the 

 wing describe a figure of 8 track in space. 



It will further be observed that the planes of the wing are as a rule 

 reversed during the down and up strokes ; nay, more, that the angles of inclina- 

 tion made by the surfaces of the wing with the horizon vary at every stage of 

 the wing's progress, this variation in the angles being accompanied by a varia- 

 tion in the curves occurring on the anterior and posterior margins, as already 

 explained. As a consequence, the wing is moving in all its parts at the same 

 time — a somewhat remarkable occurrence, and calculated, it appears to me, to 

 excite the curiosity, if it does not rivet the attention of physiologists. The wing 

 of the insect is, with few exceptions, more flattened than that of the bat and 

 bird, a circumstance which enables it, when it is made to vibrate in a more or 

 less horizontal direction, and when its planes are reversed at the end of each 

 stroke, to apply its under or ventral surface to the air when it is urged 

 from behind forwards, and its upper or dorsal one when urged from before 

 backwards (figures 3 and 4, page 338). It sometimes happens that the 

 posterior margin of the wing is rotated in an upward direction at the end 

 of the forward stroke, and in this case it is the under surface of the wing which 

 is effective during the backward stroke (vide g h ij k I of figure 19, page 351). 



* Mechanisnie du vol des insectes — comment se fait la propulsion. Eevue des Cours Scientifiques 

 de la France et de l'Etranger, 20th March 1869. 



t Fifth Annual Eeport of the Aeronautical Society of Great Britain for 1870, pages 42-47. 

 Figures 1,2; Diagrams 1-4. 



\ Artificial flight is described at page 402. 



