42 
Engineering,’’ suggests a new field for the 
profession, analogous to marine engineer- 
ing and which may in the future prove al- 
most as important. So long as the spherical 
balloon was the sole method of rising in 
the air, the technical questions involved be- 
longed to physics and chemistry rather 
than to engineering, but with the advent 
of the dirigible balloon and the aeroplane, 
the mechanical engineer was called upon 
to provide the lightest possible motive- 
power and to design the framework of the 
balloon and the supporting surface of the 
aeroplane to sustain the greatest stresses 
with the least weight. 
The determination of the meteorological 
conditions at different heights and places 
and under all weather conditions belongs 
to the meteorologist and his observations 
originally made in the interest of pure sci- 
ence now become of practical value. The 
necessity of knowing the conditions which 
may be encountered by air-craft in their 
voyages through space of three dimensions 
will ultimately lead to the construction of 
flying charts at different levels but 
Otherwise similar to the sailing charts 
for the ocean. A beginning has already 
been made by the writer, who has pub- 
lished a series of twenty-four charts based 
on material collected by the Blue Hill 
Observatory in the United States and 
over the Atlantic Ocean. Since in the air 
as on the earth it is not the average, but 
the individual thing, which happens, an 
attempt is made to specialize for the time 
of day and season and also to show the 
sequence of wind-changes aloft which ac- 
company different barometric conditions 
at the ground. A knowledge of the wind, 
which varies with both place and level and 
depends upon the meteorological situation, 
has a far greater importance for the air- 
man than for the navigator, whose vessel 
rests on a dense and relatively stationary 
SCIENCE 
[N.S. Vou. XXXV. No. 889 
medium. In general, the velocity of the 
wind increases with height and its direction 
becomes more constant, but the observa- 
tions at Blue Hill seem to indicate that the 
gusts of wind, while increasing with the 
average velocity, decrease as we rise in the 
free air and are greatest near the ground 
in northwest winds, where they may be 
double the average speed. In experiments 
there by Mr. 8. P. Fergusson, as many as 
ten pulsations per second were recorded by 
the most sensitive anemometers on a wide 
time-sheet. The uprush of air under cumu- 
lus clouds, which are especially strong 
when they become cumulo-nimbus or 
thunder-clouds, are dangerous to all air- 
eraft that depend on dynamic equilibrium, 
as are the eddies termed by aviators “‘holes 
in the air,’’ which are produced by super- 
posed currents having different velocities 
or directions. It is possible for an aero- 
plane to fall when traveling with the wind 
if the gust greatly outstrips the mean ve- 
locity of the current that carries the aero- 
plane, which our experiments show to be a 
frequent occurrence, because its relative 
motion through the air, due to its motor, 
and therefore the upward component which 
furnishes support, is decreased by the in- 
ertia of the flying-machine preventing it 
from responding to the sudden impulse. 
The same thing may happen when going 
against the wind if a sudden lull occur, 
and if the aeroplane pass abruptly up or 
down into another air stratum of different 
velocity. Such local currents and atmo- 
spheric eddies, which have long been known 
to meteorologists from the behavior of their 
kites and balloons, will now be studied wm 
situ and with danger by the aviator. Some 
of these disturbances may be counteracted 
by automatic control of equilibrium, but 
generally by increasing the speed and size 
of the machine and so rendering it less 
susceptible to the influence of those per- 
