Ocroser 25, 1918] 
yet been designed, and improvements are 
needed in them all. Scientific men in all 
countries, including our own, have the matter 
under study; and the results so far accom- 
plished are truly wonderful. In the use of 
airplanes for observation purposes, or in 
squadron formation in making attacks, it is 
essential for the men in the machine to com- 
municate with the ground. Many systems are 
in use, involving the application of light sig- 
nals, wireless telegraph, ete. Obviously the 
proper instrument would be the wireless tele- 
phone, and that is surely coming, and soon it 
will be possible for one pilot to talk with another 
or with the commanding officer on the earth; 
and the latter can give orders to all of his ma- 
chines in the air. The objection to the use of 
all forms of wireless apparatus, telegraph or 
telephone, is that the enemy may confuse the 
signals by using the same wave-length for his 
disturbing impulses. This may be prevented 
however. Under the demands of the modern 
army, all forms of wireless have been so per- 
fected that the progress made is a source of 
surprise and wonder. In fact there have been 
made in this country certain modifications 
and improvements which are held rigidly 
secret. It is interesting to note that every 
one of these alterations in wireless operation 
was first worked out in physical laboratories, 
by trained physicists. Bomb dropping as 
practised to-day is not a scientific operation; 
there are too many variables. In spite of this, 
though, the accuracy of hits is increasing 
daily; and new processes are being developed. 
When it is seen that one method can not be 
made accurate, the next step is to devise one 
that will be. It will not be long before all the 
countries in the war will realize the fact that 
the tactics of fighting in the air are essentially 
unique, and there will be a land-service, a sea- 
service and an air-service. Both the army 
and the navy need airplanes for their opera- 
tions; but after their demands are supplied, 
there remains the wide expanse of the air 
through which attacks can be made upon the 
enemy, far away from the battle-front and the 
coast. Great Britain has recognized this all- 
important fact, and is building a great fleet of 
SCIENCE 
405 
airplanes for this new service. In this, new 
instruments, new types of machines, new guns 
and bombs are required. 
There are two main problems in connection 
with the submarine, first to locate it, second to 
destroy it. Methods of destruction are at hand 
in the shape of depth bombs; but methods of 
detection so far have not been eminently suc- 
cessful. From an airplane one can see through 
the water only to a limited depth, never more 
than twenty feet, and so the main reason why 
the seaplanes have been so successful in de- 
stroying submarines is not due to the fact that 
the observer in the airplane discovers his prey, 
but is that his machine has such great speed, 
three times that of a destroyer, that when news 
is flashed that a vessel is being attacked by a 
submarine it can often reach the spot in time 
to drop its bomb effectively. The detection of 
the presence of a submarine is a definite phys- 
ical problem; and it is not an exaggeration to 
say that at least one fourth of the physicists of 
note in England, France and this country have 
been engaged in the attempt to solve it. What 
lines of attack upon it are open? Not many. 
The submarine in motion emits certain 
sounds; can they be heard? It is a solid 
body; can one obtain an echo from it? It is 
made of iron; can this fact help through some 
magnetic action? These are the obvious lines 
of approach, but one should not hastily con- 
clude that there are not others. Without stat- 
ing, and I may not, how far successful these 
efforts of the physicists have been, I may note 
that the method which is now being tested by 
our Navy is one elaborated by a distinguished 
professor of mathematical physics. In the 
course of these extremely numerous experi- 
ments upon the submarine question several 
beautiful methods have been developed which 
after the war will have great scientific impor- 
tance; one of these, due to a French physicist, 
is one of the most interesting developments in 
physics made within a decade. Another sub- 
marine problem, which is by no means of sec- 
ondary importance, is to develop a method by 
which one submarine may communicate with 
another or with the shore. I do not think I 
