“First,” he says (exper. No. 45), “let there be a cauldron with water in it and a covered top; and let a fire be lighted under it. From the cover let a tube run upward, and place at its extremity a hollow hemisphere, in like manner perforated. Then, if a light ball be cast into the middle of the hemisphere, the vapour (steam) raised from the cauldron through this tube will lift the ball so that it seems suspended.” This is no doubt an ingenious and amusing philosophical toy, but has no further value. His next experiment, however (No. 50), is of greater importance, not only as showing a clear and distinct appreciation of the motive power of steam, but because its principle is embodied in the well-known mode of driving potters’ wheels and in the modern turbine. He says, “Let a fire be lighted under a cauldron with water in it and covered with a lid; and attach to this cauldron a bent tube with the extremity fitting into a hollow ball. Opposite to the extremity of this tube place a pivot fastened to the lid, and let the ball have various tubes communicating with it at opposite ends of the diameter, with their bendings at right angles (i.e., in opposite directions). Then when the fire is lighted, the steam passing through the first tube (i.e., from the cauldron) into the ball, will pass out through the bent tubes towards the lid, causing the ball to revolve after the fashion of dancing figures.”[8] This machine was called the Æolipile. [Illustration] In these few words we have a clear indication of the power of steam, of the nature and effect of a vacuum, and of a rotatory engine moved by this force: we thus see that the ancients knew more than has been generally admitted of the wonderful power which, in our own time, has brought about the most extraordinary changes in the seats and centres of maritime commerce, affording to mankind a facility of intercourse between different nations, while at the same time increasing the wealth, and, what is of much more importance, promoting the comfort and happiness of the human race to an extent far beyond the dreams of the most sanguine enthusiast of any age or of any country. From the uncontroverted facts here stated, there can be no doubt that Hero was the first to record, even if he did not invent, this mighty civilising instrument, and, if so, that Egypt was the land of its birth. [Sidenote: Application of science to superstitious purposes.]