1876.] 
Correspondence . 
135 
track in space, he is even now ignor- 
ant of the exadt course pursued by 
the wing. Thus he represents the 
wing as oscillating in a vertical 
direction, the down stroke according 
to him being delivered downwards 
and backwards, and the up stroke 
upwards and backwards as in fig. 5 
of present communication. In reality, 
and as I long ago pointed out, the 
wing of the insedt is made to vibrate 
in a very oblique and nearly hori- 
zontal direction, the down stroke 
being delivered not downwards and 
backwards but downwards and for- 
wards ; the up stroke being delivered 
not upwards and backwards but 
upwards and forwards , so (fig. 6 of 
present communication). This is a 
vital point. It is a physical impos- 
sibility for the wing to adt as Professor 
Marey states. The arrows in Pro- 
fessor Marey’s figure of 8 ought in 
reality to be reversed. To get a 
continuous series of figure-of-8 loops, 
or of forwards curves characteristic of 
progressive flight, the wing must, as 
I have all along maintained, descend 
and ascend in a forward direction. 
The tracings obtained by Professor 
Marey himself prove this conclusively ; 
nevertheless he has failed to divine 
their precise meaning. That the true 
action of the wing is such as I in- 
dicate is placed beyond doubt by my 
own experiments with natural and 
artificial wings published in the 
“ Transactions ” of the Linnean and 
Royal Societies, and by recent experi- 
ments described in the “ Ninth 
Annual Report of the Aeronautical 
Society of Great Britain.” 
(IV.) Letter addressed by Professor 
Marey to the French Academy of 
Sciences in reply to a Reclamation 
lodged by Dr. Pettigrew ( Comptes 
Rendus , May 16, 1870). 
“ It is with regret that I have so 
long delayed the reply to the note of 
Mr. J. B. Pettigrew of date 18th April 
last. The author of that note re- 
I claimed priority in the description of 
the figure-of-8 path pursued by the 
wing of the insedt in flight. In sup- 
port of his reclamation the author 
quoted several passages of a memoir 
which he has sent to the Academy. I 
have perused this memoir, and have 
ascertained that in point of fadt Mr. 
Pettigrew had seen before me and re- 
presented in his memoir the figure-of-8 
track made by the wing of the insedt ; 
that the optical method to which I 
had recourse is almost identical with 
his ; but that we differ entirely in 
regard to the interpretation of the 
trajedtory which we have both seen. 
Our disagreement refers to the direc- 
tion of the movement of the wing 
during its course, the cause of its 
changes of plane, and the inflexions 
of its course which I ascribe to the 
resistance of the air. Finally, gene- 
ralising his theory of the movements 
of the wing, the English author as- 
signs to the wing of the bird the same 
trajedtory as to that of the insedt, 
whilst I have shown — in my ledtures 
at the College of France, published 
last year in * Revue des Cours Scien- 
tifiques ’ — that the wing of the bird 
moves according to a kind of ellipse 
of which the great axis is nearly ver- 
tical. In presence of these differences 
I have thought it right to address my- 
self diredtly to Mr. Pettigrew, to ex- 
plain to him the complexity of the 
dispute, and to ask him bow I could 
reply to his ‘ Just Reclamation ’ with- 
out entering into a discussion which 
would unnecessarily complicate the 
question. It is only to-day that I 
have received the reply of the physi- 
ologist of Edinburgh. He holds to 
establish only ‘ that he has described 
and figured before me the figure-of-8 
track made by the wing of the insedt, 
and the spiral and undulatory curve 
which the wing of the insedt, the bird, 
and the bat describes when these ani- 
mals fly with a great horizontal velo- 
city.’ Whether this remark has been 
made by other naturalists nobody 
would venture to affirm, but in any 
case I hasten to satisfy this legitimate 
demand, and I leave entirely the pri- 
ority over myself to Mr. Pettigrew 
relatively to the question so restridted. 
I hope to be able soon to submit to 
the Academy my experiments on the 
analysis of the movements of the bird 
during flight, in order that the Academy 
may judge the value of the processes 
which I have employed in that inves- 
tigation.” 
Note. It appears to me that the 
real restridlive clause is that quoted by 
me, and not by Prof. Marey ; the clause 
alluded to having reference to the 
figure-of-8, spiral, and undulatory 
