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Show j Sounding "for Shells. Where the tide of battle has ebbed and fiowe.i. the soil of France is so full of proiecti!e th?.t a French inventor has ; devised an electrical apparatus to find thorn. As soon j? the thrifty Fren-h re- ; cover anv porr.nn of land from the in- jvader they return it at once to asrieul- tuial use. but before the soil is plowed it is neeessarv to find any sources of potential po-tential danser in the form of unexploded shells that may lie beneath. The instrument instru-ment that thev use is an adaptation of the Hushes induction balance. As described de-scribed in the proceedings of the French -Vcademy of Sciences, the apparatus is so sensitive that the operator caE detect by sound throuKh the telephone: the presence pres-ence of a fragment of shell, or even of a tin cfcn. It is also possible from the nature na-ture of the sound to distinguish between considerable masses of metal and small frasments. The Instrument has two coils of large diameter, the windings of which are on wooden frames. As is usual in tho Induction balance, no metal of any kind is used in that part of the instrument. instru-ment. The two coils, attached to a handle, han-dle, form an instrument with which the surface of the soil is explored and tested. As long as there is no metal present the mutual" induction of the primary and the secondary circuits is in a neutral state, with the result that the telephone remains slient. When fragments of shell are encountered, en-countered, even if they lie at considerable consider-able depth, their presence speaks, as it were, through the telephone. It takes two persons about an hour to test thoroughly an acre of ground, but when the work has been completed, the farmer can be sure that there is nothing left there to endanger his life or blunt his plowshare. Edison Monthly. |