1010

THEORY AND PRACTICE OF ENGINEERING.

Rook II.

carriages, and placed upon the platforms, whence they were again moved to their severalplaces of destination.

Fig. 1526.

PEBRONET’S CRANES CSED AT KEUILLY BRIDGE.

In wheel cranes we have an example in which the body receives an impulse in a directionperpendicular to the axis, and where a uniform rotatory motion is produced, the velocityof which depends on the force of the impulse, the distance of thedirection of the impulse from the axis, and the manner in which themass of the body is distributed round the axis: we must also con-sider, that the whole force of the impulse is distributed amongstthe various parts of the mass, and is transmitted to them fromthe point where the impulse is applied, in consequence ofthe cohesion of the parts, and the impossibility of onepart yielding to a force, without carrying all theother parts with it.

Another crane used by Perronet at the bridgeof Orleans, with a very simple framing, wasalso worked by a wheel, as is still thecustom throughout France : at all thequarries in the neighbourhood of Pariswheels are made use of to hoist theblocks of stone. This kind of cranerequires to be well balanced tobe effective, and in this examplegreat attention was paid tothis point.

Fig. 1527. perronet’s cranes used at Orleans bridge.

In some experiments made at the London Docks with a wheel crane worked by sixmen, a weight of 787,920 pounds was raised 7 feet in 8 hours, equal to 1916 raised on&