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 messages that can be perceived at distances of hundreds of miles. Each such message must have some identifying signal or some characteristic feature to indicate its origin just as the sending station on a telegraphic line must wire its code name along the line to the receiving station. These messages can be picked up by the airships or aeroplanes and their source determined just as a sailor on seeing a flashing or revolving light can identify the lighthouse from which it comes. Thus the airship learns the bearing of a known land station and by repeating such observations can determine its position in space. This is the only known way of navigating trackless fields of air where you are unconscious of the currents in which you are moving even though they may have velocities comparable to your own.

Because I have dwelt on these broad formative factors of this War, it must not be thought that Science has failed us in satisfying its smaller and more special demands. I could spend hours in describing how it has helped us over 41