BOOK VIII.

3i9

But to return to the stamping machines. Some usually set up fourmachines of this kind in one place, that is to say, two above and the samenumber below. By this plan it is necessary that the current which has beendiverted should fall down from a greater height upon the upper water-wheels, because these turn axles whose cams raise heavier stamps. Thestamp-stems of the upper machines should be nearly twice as long as the stemsof the lower ones, because all the mortar-boxes are placed on the same level.These stamps have their tappets near their upper ends, not as in the case ofthe lower stamps, which are placed just above the bottom. The water flowingdown from the two upper water-wheels is caught in two broad races, fromwhich it falls on to the two lower water-wheels. Since all these machineshave the stamps very close together, the stems should be somewhat cut away,to prevent the iron shoes from rubbing each other at the point where they areset into the stems. Where so many machines cannot be constructed, byreason of the narrowness of the valley, the mountain is excavated andlevelled in two places, one of which is higher than the other, and in this casetwo machines are constructed and generally placed in one building. Abroad race receives in the same way the water which flows down from theupper water-wheel, and similarly lets it fall on the lower water-wheel. Themortar-boxes are not then placed on one level, but each on the level whichis appropriate to its own machine, and for this reason, two workmen are thenrequired to throw ore into the mortar-boxes. When no stream can bediverted which will fall from a higher place upon the top of the water-wheel,one is diverted which will turn the foot of the wheel; a great quantity ofwater from the stream is collected in one pool capable of holding it, andfrom this place, when the gates are raised, the water is discharged againstthe wheel which turns in the race. The buckets of a water-wheel of thiskind are deeper and bent back, projecting upward ; those of the formerare shallower and bent forward, inclining downward.

Further, in the Julian and Rhaetian Alps 15 and in the CarpathianMountains, gold or even silver ore is now put under stamps, which aresometimes placed more than twenty in a row, and crushed wet in a long mortar-box. The mortar has two plates full of holes through which the ore, afterbeing crushed, flows out with the water into the transverse launder placedunderneath, and from there it is carried down by two spouts into the heads ofthe canvas strakes. Each head is made of a thick broad plank, which can beraised and set upright, and to which on each side are fixed pieces projectingupward. In this plank there are many cup-like depressions equal in size andsimilar in shape, in each of which an egg could be placed. Right down inthese depressions are small crevices which can retain the concentrates of goldor silver, and when the hollows are nearly filled with these materials, theplank is raised on one side so that the concentrates will fall into a large bowl.The cup-like depressions are washed out by dashing them with water. These

ls The Julian Alps are a section east of the Carnic Alps and lie north of Trieste. Theterm Rhaetian Alps is applied to that section along the Swiss Italian Boundary, aboutnorth of Lake Como.