76 TRANSACTIONS OF THE | DEC. 12, 
ping will cause its direction to be changed, first across the wind, 
and then upwards and against the current; and the living force 
that has been acquired, will carry it to a plane higher than that 
from which it started, and,for some distance against the wind, 
but never as far backwards as the point of starting. A second 
evolution like the first carries it still higher, and so on, the bird 
rising ina helical path like the windings of a stairway, but 
always falling off or making leeway with the direction of the 
wind, 
The bird may thus rise to any height. At great altitudes, if 
the currents of air are nearly or quite vertically upwards, the 
successive helices may be nearly over each other and nearly in 
the same horizontal plane, and the bird may apparently soar ‘in 
circles.” 
If we now consider that the bird, in soaring under these cir- 
cumstances, is quite relieved from muscular exertion, excepting 
the very slight efforts necessary for changing direction, and that 
these exertions may be accomplished involuntarily or uncon- 
sciously, the popular idea that some soaring birds sleep on the wing 
is not to be lightly denied. We all know that men sometimes 
sleep while performing work which is usually done by voluntary 
action and in a state of consciousness, the voluntary muscles be- 
coming for a time involuntary muscles and their efforts being 
unconsciously performed. Many ordinary movements during 
sleep are thus effected unconsciously by all animals. 
The discovery of the methods by which the most severely 
strained of all the muscles of the wing may be relieved from 
constant exertion, both in soaring and in other long-continued 
flights during migrations, may thus enable us to solve what has 
hitherto been regarded as one of the most puzzling of all the 
mechanical problems of flight. 
PRESIDENT NEWBERRY discussed the subject of soaring, and 
read extracts from Prof. Jeffries Wyman referring to the lock- 
ing and “setting ” of the joints of the wing. 
He said that, in considering the anatomy of birds’ wings and 
the function of flight, there were three elements under discus- 
sion, apart from the flapping of the wings. These were: 1, 
soaring by gyration, credit being due Prof. Trowbridge for the 
only satisfactory theory; 2, ‘‘setting” of the wings by lock- 
ing of the joints, credit for this discovery being due to Prof. 
1 This refers to interlocking of primaries, see page 19, and locking of 
winy bones, see page 75.—ED. 
