. The elements of railroad engineering . pounds are suspendedby fine steel wire Avhich passes through the eye-hole in theplate. On the shaft bottom a pail of oil is placed directlyunder each plumb-bob, which is entirely immersed in theoil to check the vibrations. When the plumb-bobs come torest, the lines which suspend them are exactly in the centerline as laid down on the surface of the ground. A transit isset up at / (the tunnel having been driven some distancefrom the foot of the shaft) and moved until both wires areexactly in the line of sight. A plug is then set on the lineat A, after whi
. The elements of railroad engineering . pounds are suspendedby fine steel wire Avhich passes through the eye-hole in theplate. On the shaft bottom a pail of oil is placed directlyunder each plumb-bob, which is entirely immersed in theoil to check the vibrations. When the plumb-bobs come torest, the lines which suspend them are exactly in the centerline as laid down on the surface of the ground. A transit isset up at / (the tunnel having been driven some distancefrom the foot of the shaft) and moved until both wires areexactly in the line of sight. A plug is then set on the lineat A, after which the instrument is moved to /vand a plugset at /, thus establishing the line. RAILROAD CONvSTRUCTION. 903 1526. Ventilation. — In clear weather, the gasesformed by the combustion of the powder used in blastingpass rapidly from the tunnel to the outer air. In heavyweather, and especially when the heading is at a consider-able distance from the portal or shaft, several hours arerequired to clear the tunnel of powder smoke. Under such.
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectrailroadengineering
