Page:Popular Science Monthly Volume 89.djvu/728

714 Popular Science Monthly ��AUOHOL

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��fELT-COV[R[B WHEtL

��WIS CUCniOMAGNfllC CtUICH IS f«STW- fD 10 HOIOR SHAfI WHEN KOBSt KtV IS Cf WiiSSfO, ClUHH IS MAGNilirtO IM WE (OIIS) AND J!RK5 TH[ REVOLVINIj DISC «fR A6MNSI IIS [AC! DISC mtREUPON DEWIVIS AIONO WITH CLUKH AND HOIOl!, CAUSING 1H( FECI WHEEUO TURN AND RUB lHE51E£l5IHP,(ilVIN0EEARESUIIANI SOUND.

��WIS EEfOROHACNETIC ClUICH IS SIAIION ARY.WHfN MOKE KEY ISBtEfASEO, II 6EC0MES ENERGIZED AND JERKS R(- VOLVING DISC AWAY FROM ClUICH, [L- [CIROMAGNEI CAUSING DISC 10 HALT A5RUPIIY. THUS 5IOPPIN6 SHORI IKE EflT WHEEL AND IIS SOUND THIS MAHES IHf MORSE SIGNA15 CLEAN CUT AND CLEAR

��ICfURING m DKIV- iNOlHELJCIIING WHEEL Fm COVER- ED RiM ON lAHER RUBS IHE SIELL STRIP

���The Bcrger apparatus showing its operation from the time that the Morse key is depressed until the vibrations are sent out

��together. Since all sounds come to the listener alike, it is obviously impossible sometimes for him to tell whether he is listening to a bell or to some strange noise of the sea.

Mr. Bcrger's sul^marinc signaling device, however, has the one great atU'antage that sounds sent out into the water can be mack- to ha\-e an>' duration desired. As long as the felt-rimmed wheel keeps rubbing on the steel strij), a steady, sustained note is sent outwaril. As is explained in the illustration above, the rul)bing of the wheel against the strip is under control of a teje- graph-key, the sender operating this just as he would one on an ordin,ir\- elec- tric telegrai)h circuit. As the first illu.s- ti.ilion on page 712 makes clear, these

��signals sent out into the water are picked up by a microphone (delicate form of telephone transmitter) mounted in a water-filled chamber in the side of the receiving vessel. The listener simpK' adjusts telephone-receivers to his ears and hears signals just as he would hear ordinary wireless telegraph mes- sages. This sound-wa\e telegraph is as truh' a wireless telegraph as the kind using electric waves.

Commander F. L. Sawyer, of the rnitc-d States Xa\>', has proposed that the Bcrger in\ention be combined with ordinary wireless telegraphy, the two together forming an effec- tive means of warning in case of fog. The fact that electric waves tra\'cl with the speed of light (i86,cxx) miles per second), or almost instantaneously, and that sound wa\-es in water travel much more slowly (4,708 feet per second), is the basis for the proposed methcxl. The electric signals and the sound-signals are sent out simultaneously by the ap- j)roaching vessels. Ths lis- tener on either boat hears the wireless signal instantly and the sound-signal a few seconds later (it having taken that long to arrive) and he can judge fairly well how far apart the r\vo vessels are — the number of sec'onds in this inter\al multiplied b>- the speed of sound in water gi\iiig the aiijiroximate distance. If the time intervening between receiving the two signals grows less and le.ss the operators know that the two vessels are approaching and may collide. A code system, composed of different letters of the alj'jhabct and indicating whate\er course the \essels are pursuing, is .ilso proposed.

Professor R. A. Fessenden has in- vented an underwater sound-signaling machine somewhat like Mr. Herger's. His contrivance, however, makes use of an electromagnetic oscillator working on one of the i>lates of a vessel's hull in place of Herger's vibrating wire. Both contrivances are elTective means of com- municating \\iili >ul>nurgi(l subm.irines.

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