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. [Illustration: FIG. 6.--AN ANCIENT JEWISH MILL.] [Illustration: FIG. 7.--AN OLD ROMAN MILL.] [Illustration: FIG. 8.--A SCOTTISH QUERN.] [Illustration: FIG. 9.--POMPEIAN FLOUR MILL, 79 A. D.] We have here several pictures of ancient mills. Figure 6 is an ancient Jewish mill. As we look at it we may recall the words, "Two women shall be grinding at a mill, the one shall be taken, and the other left."[14] Figure 7 is an old Roman mill bearing a strong resemblance to the coffee mill that is used in our kitchens. Figure 8 is a Scottish quern, a mill that may still be found in use, it is said, in some parts of Scotland. Figure 9 is an old flour mill dug from the ruins of the city of Pompeii which was destroyed by an eruption in the year 79 A. D. Figure 10 shows the construction of this interesting mill. The upper (outer) stone is shaped like an hour-glass, the upper half of which serves as a hopper; the lower half turns upon the cone-shaped lower stone and does the grinding. The mill was operated by the projecting handles, the operators walking round and round the mill. Sometimes it was turned by human power, sometimes by horses or oxen. [Illustration: FIG. 10.--SHOWING THE INTERIOR OF POMPEIAN MILL.] [Illustration: FIG. 11.--THE FIRST WATER-MILL, 50 B. C.] [Illustration: FIG. 12.--SHOWING THE INTERIOR OF THE FIRST WATER-MILL.]