BOOK X.

478

other, and are joined with five randies; these randies are two and a halfdigits thick and are placed three digits apart. Thus a drum is made, whichis a palm and a digit distant from the upright timber, but further from thecrane-post, namely, a palm and three digits. At a height of a foot and apalm above this little axle is a second small square iron axle, the thickness ofwhich is three digits ; this one, like the first one, turns in bronze or ironbearings. Around it is a toothed wheel, composed of two discs a foot threepalms in diameter, a palm and two digits thick ; on the rim of this thereare twenty-three teeth, a palm wide and two digits thick ; they protrudea palm from the wheel and are three digits apart. And around this sameaxle, at a distance of two palms and as many digits toward the uprighttimber, is another disc of the same diameter as the wheel and a palm thick ;this turns in a hollowed-out place in the upright timber. Between this discand the disc of the toothed wheel another dram is made, having likewise fiverandies. There is, in addition to this second axle, at a height of a cubitabove it, a small wooden axle, the journals of which are of iron ; the endsare bound round with iron rings so that the journals may remain firmly fixed,and the journals, like the little iron axles, turn in bronze or iron bearings.This third axle is at a distance of about a cubit from the upper small cross-beam ; it has, near the upright timber, a toothed wheel two and a half feetin diameter, on the rim of which are twenty-seven teeth ; the other part ofthis axle, near the crane-post, is covered with iron plates, lest it should be wornaway by the chain which winds around it. The end link of the chain is fixedin an iron pin driven into the little axle ; this chain passes out of the frameand turns over a little pulley set between the beams of the crane-arm.

Above the frame, at a height of a foot and a palm, is the crane-arm. Thisconsists of two beams fifteen feet long, three palms wide, and two thick,mortised into the crane-post, and they protrude a cubit from the back of thecrane-post and are fastened together. Moreover, they are fastened by meansof a wooden pin which penetrates through them and the crane-post ; thispin has at the one end a broad head, and at the other a hole, through whichis driven an iron bolt, so that the beams may be tightly bound into the crane-post. The beams of the crane-arm are supported and stayed by means oftwo oblique beams, six feet and two palms long, and likewise two palms wideand thick ; these are mortised into the crane-post at their lower ends, andtheir upper ends are mortised into the beams of the crane-arm at a pointabout four feet from the crane-post, and they are fastened with iron nails.At the back of the upper end of these oblique beams, toward the crane-post,is an iron staple, fastened into the lower sides of the beams of the crane-arm, inorder that it may hold them fast and bind them. The outer end of eachbeam of the crane-arm is set in a rectangular iron plate, and between theseare three rectangular iron plates, fixed in such a manner that the beams of thecrane-arm can neither move away from, nor toward, each other. The uppersides of these crane-arm beams are covered with iron plates for a length ofsix feet, so that a trolley can move on it.