Page:Popular Science Monthly Volume 92.djvu/648

 How the Zeppelin Raiders Are Guided by Radio Signals

An ingenious system not unlike that of the flashing light which guides mariners along the rocky coasts

��A ZEPPELIN which is sent from Ger- many to England on a bomb-drop- ping expedition must travel by the shortest route. Only a limited amount of fuel is carried in order that the load of bombs may be as great as possible. But how does the captain of the ship deter- mine that route? In time of war cities are darkened and all guiding lights are extinguished. The stars may help him.. The trouble is that he travels so fast that he would have to read them at least ten times as often as would be necessary on board a ship at sea. Again, the sky may be overcast with no stars visible at all> although a war Zeppelin capable of flying four miles high could escape by rising above the clouds.

This is very plausible to the lay mind, but perhaps too far from the real facts. Actually the darkening of cities has never prevented finding the route. Rather in- visibility of the ground due to "thick" air or actual fog, has. Even then a fairly

��true course might be steered by "dead reckoning"; i. e., by computing distance and direction from log and compass, and then tracing the results on the map. But the unknown and variable wind-drift prevents this. Measuring the earth's magnetism would prevent getting far astray, but the needed apparatus would be heavy, measurements must be very numerous, and each measurement means extremely difficult and accurate work. Radio communication was soon found to offer by far the most convenient solu- tion of the problem. The L-49, which recently fell into the hands of the French absolutely intact, had a marvelously com- plete radio equipment. Even before the war, a passenger Zeppelin, the Viktoria- Luise, kept in continuous communication with the Island of Nordeney in the North Sea while scouting near Strassburg on the upper Rhine. That was in 1912. Since then the range of a Zeppelin's radio ap- paratus has been trebled.

���A Telcfunkcn-compass sending station. Factory chimneys frequently serve as aerial sup- ports, as in this case. Germany thus effects a saving of metals valuable for other war needs

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