1875.] Aérial Locomotion. 241 
in space; secondly, to the reversal of the planes of the 
wing as the wing flies to and fro, z.e., during a revolution ; 
and thirdly, to the varying angles made by the surfaces of 
the wing with the horizon, when the wing is made to 
vibrate. 
Surely this is more than a mere coincidence ! 
Then how strangely Professor Marey has blundered as to 
the direction of the stroke, when this is vertical. ‘Thus he 
represents the wing (p. 195, fig. 82) as descending in a 
downward and backward direction, and as ascending in an 
upward and backward direction. Now this is simply a 
physical impossibility, and clearly shows that Professor 
Marey has failed to interpret the tracings obtained from the 
wing by his so-called graphic method. 
The arrows in Professor Marey’s figure-of-8 (vide figure 82), 
depicting the movements of the wing in space, should, in 
reality, be reversed. To get a continuous series of figure- 
of-8 loops, or of forward curves, characteristic of progressive 
flight, the wing must descend and ascend always in a forward 
direction, as described and figured by Dr. Pettigrew.* The 
tracings obtained by Professor Marey himself show this 
conclusively. 
At page 201 of the work under consideration, Professor 
Marey describes his artificial wing as consisting of a rigid 
main vib in front and a flexible sail behind, from which it 
follows that he is not even now aware that a natural wing, 
and a properly constructed artificial one, are flexible and 
elastic throughout. 
Professor Marey is wrong, when he states that the’ ante- 
rior margin of the wing of the insect 7s rigid. The following 
are his words :— 
“These experiments prove that the inse& needs, for the due function of 
flight, a rigid main rib and a flexible membrane. If we cover the flexible part 
of the wing with a coating which hardens as it dries, flight is prevented. We 
hinder it also by destroying the rigidity of the anterior nervure.”—P. 208. 
Dr. Pettigrew, in his memoir “On the Physiology of 
Wings,” expresses the fa¢ts in very few words :— 
‘* The wing of a flying creature. ... ts not rigid.t{ ... That the anterior 
* According to this authority, ‘‘a natural wing, or a properly constructed 
artificial one, cannot be depressed either vertically downwards, or downwards 
and backwards. It will (the writer would say ‘ does’) of necessity descend 
downwards and forwards in a curve. This arises from its being flexible and 
elastic throughout, and in especial from its being carefully graduated as 
regards thickness, the tip being thinner and more elastic than the root, and 
the posterior margin than the anterior margin.” 
+ This is again insisted upon in ‘‘Animal Locomotion,” p. 240, where Dr. 
Pettigrew remarks. when speaking of the construction of an artificial wave 
wing on the insect type, “It should be flexible and elastic throughout.” 
