30 Natural and Artificial Flight. [January, 
supposing ten strokes of the wing to be made per second, the 
total force expended per second amounts to 2 or 3 kilogram- 
metres. But as between each stroke of the wing there 
lapses one-tenth of a second, during which the bird does not 
fall, but elevates itself under the impulse that is given to it, 
five strokes of the wing are sufficient, and the force required 
will be only i or 1} kilogrammetres. Now these hypo- 
thetical calculations are very closely related in result to the 
direct anatomical investigations of M. Marey, who found, 
by exposing the great pectoral muscle, and exciting it elec- 
trically to cause motion, that the force of contraction supported 
a weight of 2 kilogrammes 380 grammes. Admitting that 
the electrical agent cannot produce so powerful a muscular 
contraction as that called forth by the will, and doubling or 
quadrupling the results obtained, there still does not result 
the force that Koster attributes to the muscle of man. 
Hypothetically, a bird capable of sustaining itself must ex- 
pend a force proportional to its weight, and consequently 
ought to possess a proportional weight of muscle. This has 
been found experimentally true, and it appears, from the re- 
searches of Hastings, published in the ‘‘ Archives Neér- 
landaises”’ for 1869, that the weight of the pectoral muscle 
is about one-sixth of the total weight of the bird. It would, 
therefore, be a natural conclusion that we should admit the 
wings of birds to possess the same velocity, and from this 
point of view the duration of the stroke will increase with 
the linear dimensions of the bird,—that is, large birds will 
make fewer strokes than small ones. M. Marey has invented 
a novel and most ingenious apparatus for the measurement 
of the frequency of the strokes of the wings of a bird, and 
the relative duration of the periods of elevation and de- 
pression: By his method the bird is made to record the 
movements of its wings, by the swelling of its pectoral 
muscle as it contracts to draw the wings downward. The 
bird flies in an inclosure 15 metres square and 8 metres high. 
The registering apparatus (Fig. I) consists of a revolving 
blackened cylinder, upon which a style traces a crenulated 
line corresponding to the motions of the wings. A double 
connection is established between the bird and the registering 
apparatus; one by eletricity, conveyed through two fine 
wires to contact points fastened to the wing of the bird ; the 
other by flexible India-rubber tubing, about 12 metres in 
length. This apparatus is applied to a pigeon by means of 
acorset. Under this corset, between it and the peCtoral 
muscle, is placed a small, shallow metal basin, containing a 
spiral spring, and covered by a thin sheet of rubber (Fig. 2). 
