Synchronous Signalling in Navigation (Classic Reprint)

Excerpt from Synchronous Signalling in Navigation

Synchronised signalling is based on a fact, the ascertainment of which is old in the history of scientific advance that disturbances travel with different speeds in different media. Light and other electro-magnetic disturbances (such as telegraphy or wireless may be regarded as instantaneously propagated; sound travels relatively slowly; and in water more than four times as fast as in air. These are fundamental facts which have been made the subject of accurate measurements and certainly require no further experiments to establish. They are the scientific bases of synchronous signalling. The practical basis differs somewhat accord ing as we consider its application to coastal stations, or to the prevention of collision. Re garding the first, we may say that two factors only are involved: (1) The possibility of simul taneously originating at a signal station any two or all three of these disturbances; and (2) the possibility of hearing and timing them on board ship.

No one acquainted with what has been already accomplished would hesitate in con sidering both these conditions as perfectly feasible. Fortunately we may take even a stronger position. The method has been made the subject of a practical trial by the Hydro graphic Department of the United States Navy. All three kinds of signals - wireless, submarine, and aerial - were sent out synchronously from the Nantucket Shoals Lightship. A suitably equipped vessel, receiving signals both by chronograph and stop-watch, made a cruise in hazy weather in the neighbourhood; at in tervals finding her distance from the lightship by timing the arrival of the signals. The results are shown on a chart dated 1911 The known course of the vessel and the course as defined by the signals appear as three lines which show a quite satisfactory agreement over conditions of distance varying from one to eight nautical miles.

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