Contributions of Physical Science. ook 
photographic map making, ray filters were devised for eliminating the 
effects of haze. By means of these, landscape details were clearly delin- 
eated, while without them the plates revealed little more than a bank of 
clouds. 
In the development of suitable instruments for giving the aviator 
information as to his position, altitude and speed, and for enabling the 
accurate dropping of bombs upon assigned target areas, the combined 
skill of many specialists brought results of surprising value. With a 
dynamo-generator attached to the frame of the airplane, driven by the 
air stream and with a control so perfect that in spite of the inevitable 
large variations in speed practically a constant voltage could be main- 
tained for the radio equipment, the aviator was enabled to signal or talk 
with ground stations, with other aircraft or with his companions in the 
same machine. 
In the science of acoustics many old and well-known principles have 
been revived, extended and applied in a variety of ways. Of especial 
value were those applications to sound-ranging, for locating positions, 
and even determining caliber of enemy guns. Moreover the observer is 
enabled to distinguish between sounds due to discharge, flight and burst- 
ing of the shell. Highly developed listening devices gave invaluable 
information in locating enemy aircraft, in detecting mining operations, 
and in submarine detection. The widely used methods of ground teleg- 
raphy, invaluable in communication, recall the early experiments long 
antedating modern radio. 
Meteorology has taken its place as essentially a new department of 
physical science, and a careful study of the earth’s atmosphere has led 
to results of the highest importance in determining wind conditions 
before and after gas attacks, in correcting data for artillery fire, in 
revealing favorable conditions for the aviator, in foreseeing conditions 
which will aid or hinder transport service and in predicting fog and rain. 
In the field of electricity the vacuum tube or electron relay has dem- 
onstrated its indispensability for countless uses; telephonic and other 
communication devices have been perfected to an astonishing degree; 
the dangers of electrostatic charges on balloon fabrics have been studied 
and methods of control devised; and the quality of small portable bat- 
teries has been much improved and their life increased. In radio com- 
munication, already highly developed before the war period, startling 
results have been realized. Closed coil reception has proved successful 
in the absence of large antenna installations, and has made possible 
satisfactory work in uni-directional sending and receiving, in triangula- 
tion and in receiving on submerged submarines even at transatlantic 
distances. Without the vacuum tube much of this important work would 
have been impossible. 
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