406 
am saying too much when I state that this has 
been solved, even for considerable distances. 
Closely associated with the airplane and the 
submarine is the balloon, either a dirigible or 
an observation one. The great problem here 
is to find a means of inflating it with some gas 
which is non-infammable. Hydrogen is now 
used in general; and, when a balloon is 
brought down in flames, it means that the hy- 
drogen has caught on fire. This problem is 
partly physical and partly chemical; and nu- 
merous experiments are now in progress, all 
being directed by university men. 
I can not leave the subject of the airplane 
and the observation balloon without referring 
to the question of maps and map-making, in 
connection with which the former are so im- 
portant. Until one has been at the head- 
quarters of an army, it is not possible to 
realize the extent to which maps are used, or 
the various types of maps required. There 
are maps showing roads, paths and trenches; 
maps for staff officers, for regimental com- 
manders, for company captains, for sergeants; 
there are maps showing the position of the 
enemy’s ammunition dumps, aerodromes, signal 
stations, anti-aircraft guns; there are maps 
showing the location of the enemy’s batteries; 
there are special maps for the use of the quar- 
termaster, ete., showing where each horse 
trough, each well, each storehouse is. Map- 
making has long been a function of engineers; 
and in this war the most marked improve- 
ments have been in the main mechanical, first 
in introducting quickly on a map the revela- 
tions made by aerial photographs, second in 
increasing the speed of production of a map. 
In many cases, entirely new sets of maps are 
made each day, each one containing the in- 
formation obtained within the preceding 
twelve hours. 
Another department of science closely con- 
nected with airplanes and balloons is meteor- 
ology. We associate this word with weather 
prediction and with uninteresting data; but 
it must be remembered that these data include 
observations of temperature, of moisture con- 
tent of the air, of air pressure, of wind direc- 
tion and velocity at different heights above the 
SCIENCE 
[N. S. Vou. XLVIII. No. 1243 
earth. A knowledge of all of these is absolutely 
essential for each day’s battle. Artillery at 
a long range is useless unless the temperature, 
the moisture content and the wind are known 
accurately. Gas attacks are controlled by the 
knowledge of winds and barometric pressure. 
The safe strata for airplanes must be known; 
and for long distance work weather prediction 
of every description is essential. So impor- 
tant is the subject that observation stations 
with competent forecasters and scientific ob- 
servers dot the battle-front at close intervals; 
and the home offices send almost hourly re- 
ports to the fleets and the coast-stations. 
What strikes a layman most forcibly when in- 
specting a meteorological station near the 
battle-line is the rapidity of operation. Only 
minutes lapse between the observations and 
the deduction of the conclusion. One realizes 
then how much meteorology has grown into 
an exact science. 
Modern artillery is a good illustration of the 
application of pure science. All of us are now 
familiar with the method by which artillery 
fire is controlled by the aid of airplanes; but 
you may not realize its wonderful accuracy. 
If the enemy’s battery is located, by any 
means, this implies that its position on a 
topographic map is known to within, say, fifty 
feet, often less. It may be at a distance of 
ten, fifteen or more miles. Then to hit it, an 
exact knowledge of the properties of the pow- 
der used and of ballistics is required. With 
this, the target is reached in an astonishingly 
short time. I have witnessed myself the de- 
struction of a German battery at a distance 
of eleven miles by a French battery of three 
thirteen-inch guns, all done within ten min- 
utes, the exact aim being secured after three 
salvoes. The perfection of the mechanism of 
the French 75 and 387 millimeter guns is 
known to us all; but we hear much less of the 
English and American guns. I can assure 
you that this is only a curious bit of camou- 
flage. Of all the numerous ways in which 
physics has been called in to assist artillery, I 
known none so interesting as is illustrated by 
anti-aircraft gunnery. The problem is most 
dificult. An airplane may be traveling at a 
