Page:Popular Science Monthly Volume 89.djvu/218

 Charting the Dangers of the Deep

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��Disentangling and measuring the depth of the submerged wire-drag after it has struck an uncharted rock. With the lead Une the discovery of this rock would have been more or less a chance. At left, the buoy or float with the upright and weight attached

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��"AST summer a submerged rock was found at the en- trance to Boston harbor, close to which one or more of our ten- miUion-d o 1 1 a r super-d re ad - noughts had repeatedly passed under the suppo- sition that the water was forty-five feet deep, whereas it was actually only twent>--three feet deep. Before that a rocky pinnacle was discovered in Alaska waters, higher than the Washington monument, lying directly in the steam- ship lane. Only seventeen feet of water covered it. These are striking examples of the valuable service rendered the world's shipping interests by the United States Coast and (".eodetic Survey.

No one branch of the C.overnment plays a more important part in the wel- fare of the coimtry than the Coast Survey. It is not only the oldest scien- tific bureau in the (iovernment, but the oldest bureau of continuous service. Although its chief work is defined as the making of navigational charts of the

��United States and outlying territory, the Coast Survey gives the man who follows the sea a complete knowledge of the coast, its nature and form, the character of the adjacent sea-bottom, the positions of reefs, shoals and other dangers to na\'igation, the rise and fall of the tides, the direction and strength ot the currents and the character and amount of mag- netic disturbance.

The chief operation in a hydrographic survey is sounding. A hand line or a sounding machine is used, dcpendingon the depth of the waters, but the compara- tively recent wire-drag, introduced by French hydrographefs and since de- veloped and impnned by the Coast Survey, has re\'olutionized hydrographic surveying. The wire-drag was first used on the Atlantic Coast in 1906, and from that time to the present one thousand, six hundred and sixty square miles have been dragged and about fi\e thousand shoals examined. On the Pacific Coast this work was undertaken in 1914. Probably one-half of the shoals examined had less dei)lh tii.ui charted.

On a mariner's chart the line of sound- ings with the lead is represented by a row of figures S|)aced more or less closely together, and with the rows of numerals

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