AN AUTOMATIC RECORDER ON THE FORTH BRIDGE.

North Otago Times, Volume XXXV, Issue 7265, 13 October 1891, Page 1

AN AUTOMATIC RECORDER ON THE FORTH BRIDGE.

Sir John Fowler hat had fitted «t the end of the south main ipan of the Forth Bridge, at whiob point the contraction and expansion joint is placed, an indioator to reoord the number of trains passing and (ho daily oontrao* tion or expansion of i-he bridge. Tho apparatus oonshta (• Engineering Bays) of a brass rod, with a penoil, attaohed to the end of tho girder, and a clock with another brass rod fixed in its axle. Round the rod in tho axle of the olook is wound a atrip of paper about 4in wide, with h weight attached to tho end. The point of this pono«l rests on thia paper, whioh is, of oourse, constantly on the move »b tho clook winds down* The result is that bb the cantilever contracts the pencil attaohed to it is pulled away ; when it expands tho penoil is pushed forward, and a curve of oontraotion and expansion is thus produced by tho movement of tho paper and pencil combined. The same principle is applied to register tho behavior of the bridge while a train is passing. When the train enters on one end of the oantilevor it pulls the far off end down so it alea pulls the pencil, and tbua a mark at light angles to the curve uf contraction and expansion is made. When it passes to the other half of tho cantilever it pushes it forward, and again a mark at right angles to the curve is made on the other side. Eaoh mark indicates a train, and thus tho simple apparatus serves three purposes. The management are at present troubled a good deal with requests for passes to inspect the bridge ; but, as walking over tbo bridge owing to the narrowness of tha side walk is attended with considerable danger, very few are granted, The speed of the trains in orossing the bridge is now limited, except the goods trains, and with them it must not exceed twenty*five miles an hour. As there ia only about 2ft Gin between the pedt'Btrian on the bridge and the flying train, it is wecm that the precaution ia wiBP. Tbo average traflio on the bridge amounts to ibout 140 traini 'Jaily,