To contrive a self-trimming lamp. Let A B C (fig. 33), be a lamp through the mouth of which is inserted an iron bar, D E, capable of sliding freely about the point E, and let the wick be wound loosely about the bar. Place near a toothed wheel F, moving freely about an axis, its teeth in contact with the iron bar, that, as the wheel revolves, the wick may be pushed on by means of the teeth. Let the opening for the oil be of considerable width, and when the oil is poured in let a small basin float upon it, G, to which is attached a perpendicular toothed bar, H, the teeth of which fit into the teeth of the wheel. It will be found that, as the oil is consumed, the basin sinks and causes the wheel F to revolve by means of the teeth of the bar, and thus the wick is pushed on. 34. _A Vessel from which Liquid may be made to flow, on any portion of Water being poured into it._ [Illustration: Diagram of apparatus as described in text] If into a vessel, provided at the bottom with an open spout, liquid is poured, the spout shall sometimes run from the first, sometimes when the vessel is half filled, and sometimes not until the whole is filled: in fine, when any proposed quantity of liquid has been poured in, the spout shall run until all is exhausted. Let A B (fig. 34), be the vessel, the neck of which is closed: insert the tube C D, air-tight, through the partition, and let it reach to the bottom of the vessel leaving only a passage for the water. Let E F G be a bent siphon, the inner leg of which extends nearly to the bottom of the vessel, while the other projects without, being fashioned in the shape of a water-spout: the curve of the siphon must be close to the neck of the vessel. In A B make an air-hole, H, near the partition and leading into the body of the vessel. If we intend the spout to run immediately on the entrance of the liquid, we must place the finger on the vent H, and the spout will run, for as the air in the vessel has no way of retreat, the liquid will rush out through the bent siphon. If we do not close H, the liquid will pass into the body of the vessel, and the spout cannot run until we again close the vent: and then, if we set the vent free, the siphon will exhaust all the liquid. 35. _A Vessel which will hold a certain quantity of Liquid when the supply is continuous, will only receive a portion of such Liquid if the supply is intermittent._