200
BOOK VI.
is broken and part of the chain or anything else should fall down ; he guidesthe bag with a wooden shovel, and fills it with water if it fails to takein the water spontaneously. In these days, they sew an iron band into thetop of each bag that it may constantly remain open, and when lowered intothe sump may fill itself with water, and there is no need for a man to act asgovernor of the bags. Further, in these days, of those men who stand onthe floor the one empties the bags, and the other closes the gates of thereservoir and opens them again, and the same man usually fixes the largehook in the link of the chain. In this way, three men only are employed inworking this machine; or even—since sometimes the one who empties thebag presses the brake which is raised against the other drum and thus stopsthe wheel—two men take upon themselves the whole labour.
But enough of haulage machines ; I will now speak of ventilatingmachines. If a shaft is very deep and no tunnel reaches to it, or no driftfrom another shaft connects with it, or when a tunnel is of great length andno shaft reaches to it, then the air does not replenish itself. In such a case itweighs heavily on the miners, causing them to breathe with difficulty, andsometimes they are even suffocated, and burning lamps are also extinguished.There is, therefore, a necessity for machines which the Greeks call7 rvevfxariKai and the Latins spiritales —though they do not give forth anysound—which enable the miners to breathe easily and carry on their work.
These devices are of three genera. The first receives and diverts intothe shaft the blowing of the wind, and this genus is divided into three species,of which the first is as follows. Over the shaft—to which no tunnel connects—are placed three sills a little longer than the shaft, the first over the front,the second over the middle, and the third over the back of the shaft. Theirends have openings, through which pegs, sharpened at the bottom, are drivendeeply into the ground so as to hold them immovable, in the same way thatthe sills of the windlass are fixed. Each of these sills is mortised into eachof three cross-beams, of which one is at the right side of the shaft, the secondat the left, and the third in the middle. To the second sill and the secondcross-beam—each of which is placed over the middle of the shaft—planksare fixed which are joined in such a manner that the one which precedesalways fits into the groove of the one which follows. In this way four anglesand the same number of intervening hollows are created, which collect thewinds that blow from all directions. The planks are roofed above with acover made in a circular shape, and are open below, in order that the wind maynot be diverted upward and escape, but may be carried downward ; and there-by the winds of necessity blow into the shafts through these four openings.However, there is no need to roof this kind of machine in those localities inwhich it can be so placed that the wind can blow down through its topmostpart.