HISTORY OF MARINE ARCHITECTURE.

131

of timber, so that this powerful beam might have been lengthened to any rea-sonable extent that was required.

“ An enormous lever was suspended from this beam, which was not onlyfixed in the earth, but was also fastened against the interior side of the city wall,to which it was attached by strong ligaments. The ancients did not terrace theirwalls as moderns have done: this method was unpractised by them, on account,perhaps, of the magnitude and height of their engines of war, which could notbe used as it were in battery, without exposing them to the fury of the besiegers,who would have dismounted, or destroyed them in a short space of time. Theyplaced on their battlements such small machines only as were easily moved fromone place to another.

“ The engine, or that part of it just described, was suspended by a rope ofgreat strength, or a chain, and being supported by its beam, could produce effectsin proportion to the distance, that the power itself was removed from the fixedpoint, or center of motion, according to the known principles of mechanicalaction. At the extremity were several grappling irons, or barbed points, attachedto chains, which were thrown upon the vessels when they came within a properdistance. Several men lowered the cross-beam, or arm, by means of tworopes, and as soon as they perceived that the claws of iron had seized theobject, they made a signal, on which, one end was immediately depressed,while the other rose, and drew the vessel to a certain height: which being done,the great cable was cut, and it was suffered to fall into the sea

The account related by Curtius of the harpago has had a very different inter-pretation given to it by some commentators and critics, from that which is gene-rally attached to it, if it were supposed to have acted either on the principlesof the corvus of Archimedes -j-, or the simple grappling iron. The harpago, saythey, was so contrived, that when in its descent it should open of its ownaccord, and when checked for the purpose of being drawn up, that it shouldcontract and seize, with an irresistible force, whatever chanced to fall withinits gripe. Lucan, in particular, briefly explains the particulars of its action.

Et quos immissi traxerunt vincula ferri,

Hos prohibent jungi conserta cadavera puppes.

* Hist, de Polyb. Liv. 1. chap. iv.

f From which it appears to have varied very trivially in its uses and effects.

S 2 The