. Elements of technology :. suspended on piv-ots placed a httle out of the centre, and toward the tubes, sothat when the lamp is full of oil, the box will hang level. Asthe oil burns out, however, the end containing the tubes willpreponderate, so as to keep the flame always near the surfaceof the oil. The annexed figures show the position of the lampwhen full, and when half exhausted. This lamp is of cheapconstruction, and is said to be extensively used in cotton millsand other manufactories in the north of England. Mechanical Lamps.—Some lamps are manufactured inFrance, in which the oil is ra
. Elements of technology :. suspended on piv-ots placed a httle out of the centre, and toward the tubes, sothat when the lamp is full of oil, the box will hang level. Asthe oil burns out, however, the end containing the tubes willpreponderate, so as to keep the flame always near the surfaceof the oil. The annexed figures show the position of the lampwhen full, and when half exhausted. This lamp is of cheapconstruction, and is said to be extensively used in cotton millsand other manufactories in the north of England. Mechanical Lamps.—Some lamps are manufactured inFrance, in which the oil is raised from a large reservoir below,to a small one near the flame, by means of a pump. This insome instances is worked by hand, and in others is carried byclock work, the motion being derived from a spring, which iswound up as often as necessary. Fountain Lamp.—The most common mode of disposing ofthe oil in large lamps, is to place the reservoir above the levelof the flame, so that the burner, or part containing the wick,. ARTS OF ILLUMINATION. 181 may be supplied in small quantities, as fast as its oil is consum-ed. These reservoirs are constructed on the principle of thebird fountain. They are open at bottom, but the oil is keptfrom running out at once, by the pressure of the reservoir commonly terminates in a neck at bottom, withan opening on one side. This neck is immersed beyond theopening, in a small cavity, which contains oil nearly on a levelwith the burners, and communicates with them by tubes. Solong as the whole of the opening is immersed, no oil can de-scend from the reservoir, because no air can enter to take itsplace. But whenever the oil in the lower cavity is consumedso far, as to sink below the upper edge of the opening, a bub-ble of air will enter the neck and ascend into the reservoir; atthe same time displacing an equal bulk of oil, w^hich descendsto feed the lamp. For convenience, the opening is command-ed by a sliding valve, and when the r
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