OctoseER 25, 1918] 
speed of 100 or 10 miles an hour, it rarely 
keeps a constant course, it may be at a height 
above the earth of 20,000 feet, nearly four 
miles. The man aiming the gun must know 
the position of the airplane and its speed, 
and then must make his calculations so that 
when his shell reaches the immense height, it 
shall be so timed as to meet the airplane. It 
is true that it is rather a question of the air- 
plane meeting some fragment of the shell, 
than the converse; but the problem is the same. 
When it is realized that numerous hits are 
recorded at heights of 20,000 feet, and when 
one hears the personal experiences of the pilots, 
it is clear that the problem has been solved 
fairly well. A former student of mine writ- 
ing to me a few days ago, after telling how he 
had “ speared his first Hun” on his first day at 
the front, added that the German shells rarely 
missed him by more than ten feet, and he 
was flying a rapid scout machine and was 
manouyering for position all the time. I am 
familiar with the French and British methods 
of aiming their guns; and, as you can yourself 
decide from reading the newspapers, they are 
not inferior to the ones used by the Germans. 
One can not speak of artillery without think- 
ing of gas shells and gas attacks. The Ger- 
mans were the first to use this hideous means 
of warfare, although it is well known that it 
was proposed to the British war office many 
years ago and the decision was reached that 
it should not be adopted. When poisonous 
gases first became a weapon, it was in the form 
of gas clouds, rolled along the ground by the 
wind, the gas having been released from 
eylinders in the front line of trenches. For 
perfectly obvious reasons this mode of gas at- 
tack was soon replaced by the use of large 
shells filled with the liquefied gas. When the 
shell was exploded by a contact- or a time- 
fuse, the gas would escape and work its action 
in all the neighborhood. There are two prob- 
lems associated with this mode of warfare: 
an offensive and a defensive one. The former 
is to make a gas which can be liquefied, is 
“not so light as to diffuse upward too rapidly, 
and which will either kill the man who 
breathes it or will in some way incapacitate 
SCIENCE 
407 
him; the latter is to make a mask or a suit of 
clothing, if necessary, which will enable the 
wearer to breath and do his work in the con- 
taminated atmosphere. We hear most of 
course about the terrors of the gases used by 
the Germans; but, if they would only describe 
to us their feelings about the gases sent them, 
our point of view would change. Some might 
even have a feeling of pity. Both the ques- 
tions, of defense and offense, are strictly sci- 
entific ones, in the main belonging to chemis- 
try. The researches undertaken in Great 
Britain, France and this country are so nu- 
merous that the truth is almost unbelievable. 
It is safe to say that to-day there are at least 
2,000 chemists in America alone working on 
problems connected with the military use of 
gas. We can well be proud of the achieve 
ments of our chemists. Among many things 
which I may say I shall select two: they have 
devised a mask for use inside a gun turret on 
our large ships where a particularly dangerous 
gas is liberated during a battle, and the masks 
supplied our soldiers are at least 20 per cent. 
better than either the British or French mask, 
and they are better than the German model. 
As another illustration of the usefulness of 
chemists in this war, one should state what 
has been done by them to render the allied 
countries and our own independent of Ger- 
many from an economic standpoint. All I 
shall do, however, will be to mention two sub- 
jects: dye-stuffs and drugs; and you know the 
rest. It should be remembered, though, that 
this is not the full story, only an interesting 
chapter. 
One of the most important military ques- 
tions, which in the end is a purely physical 
one, is that of signals. Our army is most 
fortunate in having as its Chief Signal Officer 
a man who is a doctor of philosophy in phys- 
ies, from Johns Hopkins University, Major 
General George O. Squier. He certainly 
knows his subject from the scientific stand- 
point as few military officers can know it. 
Think for a moment of the variety of signals 
required. Those to and from airplanes and 
submarines have been referred to. In addition, 
each trench, each outpost, each reserve force, 
