The wandering Arabs grind their corn in portable hand-mills which are simply two circular flat stones, one of which turns loosely on a wooden pivot fixed in the other, and is moved quickly by a wooden handle. The grain is poured through a hole in the upper stone, and the flour is collected on a cloth spread under the lower. These mills are always worked by the women. Figure 8 (p/. 2) represents a very simple hand-mill whose operating mechanism consists of a face-wheel which engages the trundle or lantern of the spindle, to the lower end of which is fastened the revolving or upper stone. The millstones are enclosed by a case.
brdigo-mill.—A hand-mill on the principle of the mortar and pestle is shown in Figure 6; this mill is used for grinding indigo. The muller or pestle is pear-shaped, with slotted base; its upper end is attached to an iron double-crank axle, to which, at its upper extremity, is added a weight adapted to the pressure required upon the muller. The indigo or other dry substance to be ground is thrown into the mortar, above the 'miller; on turning the handle on the axis the indigo in lumps falls into the grooye cut through the muller, and is thence drawn under the action of the unifier and propelled to its outer edge, within the mortar, whence the coarser particles again fall into the groove of the unifier, and are further ground under it.
Evolution the Mortar and usual construction of a mor tar does not embody the self-discharging principle, but under the stimulus of necessity the whole process became reversed: the pestle was made the stationary part, and over this the mortar was carefully fitted; for the admission of the grain a central eye was cut through the mortar, to which a handle was finally adapted. Much was gained by this arrangement. The grain, falling on the summit of the nether stone, ran into the joint between the two, where it was ground as the upper stone turned, the latter carrying with it the crushed grain, which by abrasion and gravity worked its way through and escaped, fully triturated, at the periphery of the stones. Ancient mills were made in this way; the Pompeian mill shown in Figure 4 2) is an implement of like character.
As an evidence of the value of this principle, and as an illustration of the numerous instances of reinvention, we quote the following specifica tions of a mill patented in the United States in 1829: "A pair of stones is put in operation somewhat similar to those of a grist-mill, except that the lower stone is the runner, instead of the upper one, and the face of the upper stone is concave, and the lower one convex, that they may clear themselves the more readily, and thereby facilitate the grinding. The acclivity of the face of the nether stone forms an angle with the horizon of about thirty degrees, and that of the tipper a greater angle, to receive the articles to be ground, while the stones may run quite close at their peripheries. The upper stone has a large eye and is surmounted by a hopper."
The or which is operated by the impulsive force of the feet of men, is shown in Figure 9. It consists of an inclined wheel, to whose face cross-strips of wood are fastened radially at proper distances apart, to prevent foot-slipping. The under side of the wheel is provided with teeth, which engage with the cogs of a trundle, turning the horizon tal shaft and the wheel at its extremity, which, in turn, engages with the trundle of the vertical shaft, causing it to revolve, together with the mill stone on the upper end of the shaft. The hopper conducts to the eye of the millstone the grain, which, when ground, passes out from the stones by the spout, as seen in the illustration. Rich gives a picture 5) from a marble in the Vatican of the nrola asinaria, or machinaria, a mill worked by cattle instead of by men.
mills, denominated " camp-mills," have some times been taken with armies as a part of their necessary equipment. Some of these mills are of stone, while others are constructed with a notched cone, which revolves like that of a coffee-mill. They are occasionally so constructed that they can be propelled by the wheels of the carriages on which they are placed, but they are more frequently driven by horses or by men. The portable army-mill (fig. 7), a French invention, stands on a tripod and is driven by two men at the crank-handles. As the material is ground it falls into the suspended sack. Four of these machines, packed in two boxes, make up a load for a mule on the march.
mills which receive their motion from the impulse of water are designated as water-mills. Very little is known concerning the application of water-power for the purpose of grinding grain in ancient times. The following epigram of Antipater, a contemporary of Cicero, implies that water-mills in his day were not common in Europe : " Cease your work, ye maids, ye who labored in the mill; sleep now, and let the birds sing to the ruddy morning, for Ceres has commanded the water nymphs to perform your task; these, obedient to her call, throw them selves on the wheel, force round the axle-tree, and by these means the heavy mill." Vitruvius, who was a prolific writer on a variety of subjects, informs us that water-mills were in use in the time of Augustus, and that for raising water there were employed wheels which were driven by being trodden upon by men. Palladins, who lived in the fourth century of our era, advises the building of mills on possessions that have running water, so that corn may be ground without men or cattle. More than three cen turies' after Augustus there were three hundred cattle-mills in Rome, whose use, it seems, as well as that of hand-mills, was regulated by law. Public water-mills were not employed, however, until near the close of the fourth century, and during the following century they became so com mon that strict laws were required to regulate the use of the water drawn from the canals which supplied the city.