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BOOK VI.

sometimes on working days, and are thus not always near the pump, and asthe pump, if necessary, must continue to draw water all the time, a bell ringsaloud continuously, indicating that this pump, or any other kind, is uninjuredand nothing is preventing its turning. The bell is hung by a cord froma small wooden axle held in the timbers which stand over the shaft, anda second long cord whose upper end is fastened to the small axle is loweredinto the shaft; to the lower end of this cord is fastened a piece of wood ;and as often as a cam on the main axle strikes it, so often does the bell ringand give forth a sound.

The third pump of this kind is employed by miners when no river capableof turning a water-wheel can be diverted, and it is made as follows. Theyfirst dig a chamber and erect strong timbers and planks to prevent the sidesfrom falling in, which would overwhelm the pump and kill the men. Theroof of the chamber is protected with contiguous timbers, so arranged thatthe horses which pull the machine can travel over it. Next they again set upsixteen beams forty feet long and one foot wide and thick, joined by clampsat the top and spreading apart at the bottom, and they fit the lower endof each beam into a separate sill laid flat on the ground, and join these by apost ; thus there is created a circular area of which the diameter is fiftyfeet. Through an opening in the centre of this area there descends anupright square axle, forty-five feet long and a foot and a half wide and thick ;its lower pivot revolves in a socket in a block laid flat on the ground in thechamber, and the upper pivot revolves in a bearing in a beam which is mor-tised into two beams at the summit beneath the clamps ; the lower pivot isseventeen feet distant from either side of the chamber, i.e., from its front andrear. At the height of a foot above its lower end, the axle has a toothed wheel,the diameter of which is twenty-two feet. This wheel is composed of fourspokes and eight rim pieces ; the spokes are fifteen feet long and three-quarters of a foot wide and thick 17 ; one end of them is mortised in the axle,the other in the two rims where they are joined together. These rims are three-quarters of a foot thick and one foot wide, and from them there rise andproject upright teeth three-quarters of a foot high, half a foot wide, and sixdigits thick. These teeth turn a second horizontal axle by means of a drumcomposed of twelve rundles, each three feet long and six digits wide andthick. This drum, being turned, causes the axle to revolve, and around thisaxle there is a drum having iron clamps with four-fold curves in which catchthe links of a chain, which draws water through pipes by means of balls.The iron journals of this horizontal axle revolve on pillows which are set inthe centre of timbers. Above the roof of the chamber there are mortisedinto the upright axle the ends of two beams which rise obliquely ; the upperends of these beams support double cross-beams, likewise mortised to theaxle. In the outer end of each cross-beam there is mortised a small woodenpiece which appears to hang down ; in this wooden piece there is similarly

17 The dimensions given in this description for the various members do not tally.