FIG. 4.—THE SLAB-MILL.
The mortar and pestle were followed by the slab-mill (Fig. 4). Here the grain was ground by being rubbed between two stones. Dr. Livingstone, the great African explorer, gives the following description of a slab-mill which he saw in operation in South Africa. "The operator kneeling grasps the upper millstone with both hands and works it backwards and forwards in the hollow of the lower millstone, in the same way that a baker works his dough. The weight of the person is brought to bear on the movable stone and while it is pressed and pushed forward and backward one hand supplies every now and then a little grain to be bruised and ground."
FIG. 5.—THE UPPER AND NETHER MILLSTONE.
As we have seen, the primitive miller gradually learned that the pestle did better work when it fell with a twirling motion. This little bit of experience led to important results in the development of the mill. If the grinding were done better with a twirling motion, why not have as much of the twirling motion as possible? Why not make the upper stone go round and round? This was what was done. The upper stone was caused to turn round and round. The wheel-mill, the mill of the upper and nether millstone (Fig. 5), was invented. When and where it was invented we cannot tell for it was in use among all civilized peoples before history began to be written. There were many kinds of wheel-mills among the nations of antiquity and in principle they were all alike in construction. How they worked may be learned by studying Figure 5 which represents a mill used in ancient India. The upper stone is placed upon the pivot projecting from the center of the lower (nether) stone, and caused to revolve by means of the handle. The grain when placed in the hollow at the center of the upper stone (Fig. 5) works its way down between the stones and comes out at the circumference ground, bran and flour together. The mill was fed with grain by the operator. The first hopper was a human hand.
FIG. 8.—A SCOTTISH QUERN.