SEPTEMBER 10, 1897. ] 
height of the migratory flight of the smaller 
birds. Of course, if the dimensions were 
greater than those assumed, the altitudes must 
be correspondingly increased, but the largest 
bird, whose distance was determined by the fo- 
cal adjustment already described, had an alti- 
tude above sea-level of 
(1321 x sin 20°) + 235 = 687 feet, 
and was certainly much lower than the smaller 
birds. 
The speeds can be roughly estimated from the 
times of transversing the lunar diameter (297.5). 
This time was on the average about one-half 
second, giving 
velocity = si >< 4 ft. per 4 sec. 
= 98.4 feet per second, 
= 67 miles per hour. 
But the swiftest flights, with every allowance 
for the difficulty of their estimation, were at 
least twice as rapid, which, if the distance were 
the same, would imply a velocity of at least 134 
miles per hour. Some of the swifter trajectories 
may have belonged to very small birds at lower 
altitudes and smaller distances, but I have al- 
ready assumed a size which is nearly that of our 
smallest birds. Any increase in the estimate of 
size enlarges that of distance and velocity. I 
am not ready to admit the probability of an er- 
ror of judgment in the estimation of apparent 
sizes of as much as 100 per cent, and I haye al- 
ready increased the more yulnerable time-esti- 
mate for the swiftest flight from 0.15 to 0.25 
seconds. Judging from the appearance of many 
of these darting specks, and with every allow- 
ance for errors of estimation, I am of the 
opinion that some of these apparent velocities 
are real, and that certain small birds (not the 
swifter swallows, humming birds and swifts, 
for these have all gone a month before the 
dates in question) can maintain a flight of 100 
miles per hour without being stripped of their 
feathers. 
In Science for January 1, 1897 (Vol. 5 N. 
S., p. 26), Mr. H. H. Clayton gives the height 
of a flock of ducks, flying southwest in Decem- 
ber, as 958 feet above the Neponset valley, and 
the velocity as 47.8 miles per hour; and in 
SCIENCE for April 9, 1897 (Vol. 5 N. S., p. 585), 
SCIENCE. 
411 
the same observer gives the height for a flock 
of geese, migrating northeastward in March, 
as 905 feet above the Neponset valley, or 960 
feet above sea-level, and the velocity of flight 
as 44.3 miles per hour. It thus appears prob- 
able that the larger birds migrate at a lower 
altitude than the smaller ones, and at not over 
half the speed of the swiftest flights. 
Even more remarkable than the speed of 
migration are the psychological problems in- 
volved in these semi-annual movements of enor- 
mous multitudes of creatures. There was, to 
me, something awe-inspiring in this spectacle 
of a throng of tiny beings launching out into 
the unknown deep, in pale moonlight and 
through the hours commonly given to sleep, 
flitting swiftly and unerringly to a far-off goal, 
while beneath, and heeding them not, slum- 
bered a dreaming world. What mighty im- 
pulse of daring is this which can transform a 
timorous sparrow, content all day to hop from 
bough to bough near to its nest and mate, into 
a bold adventurer, starting out, Columbus-like, 
on a voyage of discovery? If it were a matter 
of individual courage and wisdom, we men 
might shrink from the comparison—the ardor, 
the inerrancy, are so superhuman. Rather 
must we liken the migratory impulse to an ir- 
resistible force, drawing the winged wayfarers 
into its current, and bearing them they know 
not whither. It must not be forgotten that for 
the young birds, constituting no small number 
of the host, this journey is absolutely new, and 
not the result of experience. Ifthe movement 
were the result of knowledge and trust, we 
might well exclaim: Oh to be as confident of 
eternal beneficence, and as full of foresight as 
are these little wanderers! 
FRANK W. VERY. 
LADD OBSERVATORY, 
PROVIDENCE, R. I., September 3, 1897. 
SCIENTIFIC LITERATURE. 
Year-book of the United States Department of 
Agriculture, 1896. [1897.] 
In the preface to this volume, Mr. Charles 
W. Dabney, Jr., remarks that it falls far short 
of the ideal set for it, and regrets that it was 
not possible to give it more ‘editorial revision’ 
than it has received. We may all hope with 
