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Now it appears from the Appendix , Tab. II.,p. 7, that a rope one inch in circumference, iscapable of sustaining a strain of 21 cwt., andtherefore a rope 3 inches in diameter, or 9.42inches in circumference, will sustain a weight

of. 27350 lbs.

A rope 6 inches in circumference . 11088

Hence, the 6 floor cables will sustain 164100and the 2 suspension cables . . 22176

These are the tensions which the ropes cansafely support without risk ; and, consequently,the floor cables K K, fig. 4, alone, have abundantstrength to sustain all the strains to which theymay be subject.

The manner in which rope work was appliedin the passage of the Tagus , in 1812, by the lateLieut.-Colonel Sturgeon of the Staff Corps, andother intelligent and distinguished men, toge-ther with the use afterwards made of cables inthe passage of the Adour, as described at pages85 and 202, are instructive examples of the con-venience and efficacy of such expedients.

One of the principal arches of Trajan’s bridgeacross the Tagus , at Alcantara, having beendestroyed by the French , Lord Wellington foundit necessary to direct that a communicationacross that bridge should be re-established, forthe purpose of bringing up artillery and stores