When a fire is kindled on an altar, figures shall be seen to dance: for the altars must be transparent, either of glass or horn. Through the hearth of the altar (fig. 70), a tube is let down turning on a pivot towards the base of the altar, and, above, on a small pipe which is attached to the hearth. Communicating with, and attached to, this tube are smaller tubes lying at right angles to each other, and bent at the extremities in opposite directions. A wheel or platform on which the dancing figures stand, is also fastened to the tube. When the sacrifice is kindled, the air, growing hot, will pass through the pipe into the tube, and be forced out of this into the smaller tubes; when, meeting with resistance from the sides of the altar, it will cause the tube and the dancing figures to revolve. 71. _A Lamp in which the Oil can be raised by Water contained within its Stand._ [Illustration: Diagram of apparatus as described in text] The construction of a lamp-stand, such that, if a lamp is placed upon it, whenever the oil fails, a supply shall be poured into it from the handle to the amount required, though no vessel is placed upon the lamp from which the oil can flow into it. Let the lamp-stand be constructed with a triangular pedestal, like a pyramid, A B C D (fig. 71), hollow and provided with a partition E F. Let G H, which must also be hollow, be the shaft of the lamp-stand, and above this shaft place a hollow cup, K L, capable of containing a considerable quantity of oil. From the partition E F, and fitting closely into it, a tube, M N, must extend upwards, leaving a passage for the air between its extremity and the covering of the cup, K L, on which the lamp is placed. Through the plate K L insert another small tube X Q, a passage being left for water between it and the bottom of the cup: the tube X Q must project a little above the plate K L, and into the projecting part another pipe P is tightly fitted, closed at its upper extremity, and passing through the bottom of the lamp so as to be included within it, that there may be no projection outside. To P solder another pipe, extremely fine, communicating with it, and reaching to the extremity of the handle, so that its stream will be carried into the body of the lamp; this pipe must have an orifice like the others. Under the partition E F let a tap be soldered leading into the chamber C D E F, so that, when it is opened, the water in the chamber A B E F will pass into C D E F. In the plate A B let a fine hole be perforated through which A B E F may be filled with water; the [air] contained in it will pass out through the same hole. We now remove the lamp and fill the cup with oil through the pipe X Q, the air escaping through M N, and again through an open cock in the bottom C D, when any water in C D E F has first flowed out. The lamp having been placed on the top by means of the sliding tube P, when it is required to pour in oil, we must open the tap in the plate E F,