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DESCRIPTION OF

Secondly, They fly out and are suspended in theair. Thirdly, they hang or jut over. Fourthly,they are supported above the ground.

NOTE.

These terms are to be understood, as chastely ap-plying only to this sort of Bridge in particular, as itdiffers wholly from the ancient military flyingBridges, which were constructed of pontons, leatherboats, beams, hollow casks, blown bladders, andthe like, commonly called pont volant, or pons duc-tarius.

PROP.2.

PRINCIPLES. 1st, The principles of thisBridge, as a whole, are founded on the Lever, No. 1,

SCHOLIUM .

Each half Bridge, before it is united in the centre,is to be considered one body ; then the fulcrum, orprop, if it were intended to move, would be be-tween the weight, which is the abutment, and thepower, which is the projecting arm of the halfBridge.

COROLLARY.

Therefore the abutment, on all occasions, must beof such weight as will be more than sufficient tocounterpoise the said projecting arm while building,and also all the men and materials employed in theerection of the same.