SCIENCE AND ITS APPLICATION TO MARINE PROBLEMS. | 
recorded up to 200 miles, and it is probable that, with charges of mode- 
rate amount, explosions occurring as far away as 500 miles can be 
readily recorded. Based on these results, a system of sound ranging 
under water was developed. 
Four hydrophones were laid out 5 miles apart along a base line in 
deep water a mile or two from the shore, and, in addition, two pilot 
hydrophones were placed along a line at right angle to the base he, 
the one 5 miles out, and the other at twice that distance. Cables were 
laid frum the hydrophones to a recording instrument situated in a 
shore station. Four of these stations were installed at different places 
ulong the east coast of the British Isles, and other stations are now in 
progress of installation. With such sound-ranging systems, the shock 
of distant explosions occurring under water affect the various hydro- 
phones in turn, and as time intervals can be read to two or three thou- 
sandths of a second with the apparatus now in use, it is possible to 
measure with accuracy the time intervals between the times of arrival 
of a sound wave at the different hydrophones.° With the measurements 
of these time intervals it is a simple matter to deduce the position of 
the point at which the explosion setting up the wave is located. .Up 
to 50 miles, the location of an explosion under water can be determined 
to within a few hundred yards by a single station, but for accuracy 
the co-operation of two stations would be necessary: to locate explosions 
at greater distances. Within operable ranges a ship can be given its 
position by sound-ranging more accurately than by directional wireless, 
or by any other known method. Explosions of mines or torpedoes at 
any point in the North Sea can easily be located by stations situated in 
Great Britain. ; 
In the war, during the bombardment of the Belgian. coast, it was a 
eommon thing for a monitor to proceed in a fog to a position some 
miles from the coast, and, by dropping depth charges, have its position 
accurately determined from stations on the coast of HEngland. So 
accurately was this done that it was found, when the monitor’s guns were 
trained in selected directions, objectives several miles inland could be 
hit with regularity, and with a minimum expenditure of ammunition. 
(i) Helium.—Shortly after the commencement of the war, it became 
evident that if helium were available in sufficient quantities to replace hydro- 
gen in naval and military airships, the loss in life and equipment arising 
from the use of hydrogen would be enormously lessened. Helium is most 
suitable as a filling for airship envelopes, in that it is non-inflammable 
and non-explosive, and, if desired, the engines may be placed with the 
envelope. By its use, it is possible to secure additional buoyancy by 
heating the gas—electricity or otherwise—and this fact might possibly 
lead to considerable modifications in the technique of airship mancuvres 
and navigation. The loss of gas from diffusion through its envelope 
is less with helium than with hydrogen, but, on the other hand, the lifting 
power of helium is about 10 per cent. less than that of hydrogen. 
It was known that supplies of natural gas containing helium in 
varying amounts existed in America, and it became evident, from the 
preliminary investigations made by Sir Richard Threlfall, and from 
calculations submitted by him as to the cost of production, transporta- 
tion, &e., that there was substantial ground for believing that helium could 
be obtained in large quantities at a cost which would not be prohibitive. 
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