Another great discovery of which the date and the maker are equally unknown is referred to in only one of the ancient records available to us. It was seen that all along the eastern horizon, from north to south, stars rise, and all along the western horizon, from north to south, stars set. That is what was seen; it was the fact observed. There is no hindrance anywhere to the movement of the stars--they have a free passage under the Earth; the Earth is unsupported in space. That is what was _thought_; it was the inference drawn. Or, as it is written in Job xxvi. 7, "He (God) stretcheth out the north over empty space, and hangeth the earth upon nothing." The Earth therefore floats unsupported in the centre of an immense star-spangled sphere. And what is the shape of the Earth? The natural and correct inference is that it is spherical, and we find in some of the early Greek writers the arguments which establish this inference as clearly set forth as they would be to-day. {17} The same inference followed, moreover, from the observation of a simple fact, namely, that the stars as observed from any particular place all make the same angle with the horizon as they rise in the east, and all set at the same angle with it in the west; but if we go northward, we find that angle steadily decreasing; if we go southward, we find it increasing. But if the Earth is round like a globe, then it must have a definite size, and that size can be measured. The discoveries noted above were made by men whose names have been lost, but the name of the first person whom we know to have measured the size of the Earth was ERATOSTHENES. He found that the Sun was directly overhead at noon at midsummer at Syene (the modern Assouan), in Egypt, but was 7° south of the "zenith"--the point overhead--at Alexandria, and from this he computed the Earth to be 250,000 stadia (a stadium = 606 feet) in circumference.