1875.} Aérial Locomotion. 239 
1867, have been reproduced by Professor Marey in a variety 
of forms since December, 1868. They are reproduced in a 
collective form in Professor Marey’s work already referred 
to, published in 1874. 
The importance of the figure-of-8 and wave movements 
cannot be over estimated, and no one appears to be more 
keenly alive to their value than Professor Marey himself. 
When speaking of the figure-of-8 made by the wing in 
space, originally discovered by Dr. Pettigrew by the aid of 
the optical method, Professor Marey remarks :— 
““ We have seen, when treating of the mechanism of inseé& flight, that the 
fundamental experiment was that which revealed to us the course of the point 
of the wing throughout each of its revolutions. Our knowledge of the 
mechanism of flight naturally flowed, if we may so say, from this first 
notion.”’* 
Professor Marey here admits that his knowledge of flight 
is derived from the figure-of-8 revealed by the optical 
method ; but he admitted, as already stated to the French 
Academy of Sciences, in May, 1870, that the optical method 
to which he had recourse was nearly identical with that 
which Dr. Pettigrew employed, and that in reality Dr. 
Pettigrew had seen before him, and delineated the figure- 
of-8 track made by the wing of the insect in flight. 
If, however, Dr. Pettigrew was the first to observe, 
describe, and delineate the figure-of-8 made by the wing in 
space; and if, as Professor Marey states, his knowledge of 
the mechanism of flight ‘‘naturally flowed . . . from this 
first notion,” then it is quite evident, even according to 
Professor Marey’s own showing, that the discovery of the 
true principles of flight was made by Dr. Pettigrew, and not 
by him. This follows as an inevitable sequence. 
It is easy to extend a discovery once made, but the true 
discoverer is he who first describes and delineates the 
fundamental principle, and in the present instance that 
is unquestionably Dr. Pettigrew. 
Dr. Pettigrew not only described and delineated the 
figure-of-8 and waved track made by the wing in space; 
he also described and figured the several changes of plane 
occurring in the wing during an entire revolution. 
To him, moreover, is to be traced the important discovery 
of the torsion and forward action of the wing both during the 
down and the up strokes. The torsion and forward a¢tion 
of the wing are indispensable in flight. 
The body in flight is dragged forward, not pushed forward ; 
* Animal Mechanism, p. 234. 
VOr. V.. (N.S.) 2H 
