Page:Popular Science Monthly Volume 92.djvu/650

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��Popular Science Monthly

��In actual operation the sending station mechanically rotates its switch and sends its dots as continuously as a lighthouse with a rotating lantern flashes out beams of light. But there is a short stop before each new rotation, which commences with the first dot flashed by the north-pointing

���Intersecting lines from sending stations tell a Zeppelin commander his position accurately

antenna. During this short stop an- other but different signal is sent — a non- directional signal which is flashed over all the antennae and which is heard clearly and loudly in any direction. This signal identifies a station by giving its name or its number and supplies the in- formation that in another moment an- other cycle of dots will be sent out toward east, south, and west, commencing at the north. The aircraft commander thereupon sets the hand of his stop watch to the north. He may press the starting button as soon as he hears the first dot, and the stopping button as soon as he hears the weakest dot, or he may press the button at the strongest dot. In actual practice, he pushes the button at the dot immediately following the weakest (or strongest) signal. The difference in loud- ness is considerable from dot to dot. Indeed, the loudness progresses or de- creases around the circle of the compass, depending upon the direction in which one reads.

Imagine what a sensation it must be to be up in a Zeppelin high over an impene- trable cloud bank, the sky overhead obscured by the bulk of the gas bag, and for these reasons all the laiulinarks by which a man ordinarily locales himself obscured. Yet from somewhere beyond

��the clouds beneath comes that clear radio call indicating that in this direction at least lies a home station. The beacon is welcome. All the Zeppelin commander needs to do now is to tune a bit differently and go through the same performance with another automatic station. In a minute or two he has read on his stop watch dial his direction rela- tive to two different stations whose identity he knows. Drawing lines in these two directions from the locations of these stations on his map, he sees his own location plainly marked on the same map at the point where both lines intersect. More he could hardly demiand. But he may repeat the procedure many times in order to check up his location as frequently as the rapid progress of his craft demands. In peace time the range was in- tentionally cut down to fifty miles in order to prevent interference with regular wireless traffic. But in war, especially during a raid, a vastly greater amount of current may pass through the switches and the antennae may be worked to full capacity.

Although the Zeppelin's long range Telefunken compass uses the same theo- retical principles as the Bellini-Tosi method; that is, that parallel aerials result in loudest signals, the Bellini-Tosi method is apparently ill- adapted to Zep- pelins. The Telefunken plan seems prob- ably the one universally used.

��Fishing Electric Wires Through Tubes in Fixtures

WHEN fishing wires through a fix- ture, which has a sharp angle, a piece of chain A from a pull chain socket can be used to good advantage. If a wire is used it may get caught at point B, while the flex- ible chain readily passes around this bend. A strong cord can then be attached to the wire which is easily drawn through the fixture.

���A chain pull used to draw wire into electric fixtures

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