68. _A Shrine over which a Bird may be made to revolve and sing by Worshippers turning a Wheel._ [Illustration: Diagram of apparatus as described in text] The construction of a shrine provided with a revolving wheel of bronze, termed a purifier, which worshippers are accustomed to turn round as they enter. Let it be required that, if the wheel is turned, the note of the black-cap shall be produced, and the bird, standing on the top of the shrine, turn round as well; while, if the wheel is turned [in the opposite direction], the black-cap neither sings nor revolves. Let A B C D (fig. 68), be the shrine and E F an axis extending across it, capable of revolving freely, to which the wheel H K, which is to be turned round, is attached. Let two other wheels be attached to the axis, in the interior of the shrine, L and M, of which L has a pulley, and M is a wheel with rays. Round the pulley a cord is wound, from the extremity of which is suspended a vessel N, shaped like a conical oven, and provided with a tube X O, terminating in a small pipe which produces the note of a black-cap: under the conical vessel N must be placed a vessel of water. From the top of the shrine let fall a small axis S T capable of revolving freely: at the extremity S let a black-cap be placed, and at T a wheel with rays, the rays of which are implicated with, or take into, the rays of the wheel M. It will be found that, when the wheel H K is made to revolve, the cord is wound round the pulley and raises the conical vessel N; but, if the wheel is let go, N descends by its own weight into the water and produces the sound by the expulsion of the air. The black-cap turns round at the same time owing to the revolution of the wheels. 69. _A Siphon fixed in a Vessel from which the Discharge shall cease at will._ [Illustration: Diagram of apparatus as described in text] There are certain siphons which, when placed in vessels, flow until the vessels are emptied, or the surface of the water has sunk to the level of the outer orifice of the siphon. Let it be required that the discharge shall suddenly cease whenever we wish. A B (fig. 69), is a vessel containing a siphon, C D E, the inner leg of which is bent upwards as at C F G. Let a vertical rod H K be fixed, on which another, L M, works as a lever-beam: from L M extends another rod, M N, moving on a pivot, and provided at the extremity N with a vessel large enough to encircle the bent portion of the siphon F G. On the rod L M suspend a weight at L, so that the encircling vessel is raised above the upward bend of the siphon, and the siphon flows. When we wish the discharge to cease, we have only to remove the weight at L, and the vessel at N will descend and encircle the bend G C, so that the siphon will cease to flow. If it is desired that the stream should continue, we must again suspend the weight. 70. _Figures made to dance by Fire on an Altar._ [Illustration: Diagram of apparatus as described in text]