The simple lamp, of w bieh we have spoken. with a flat dish of oil, is very impel fact. The oii is habie to be spill ed, and the oil vessel intercepts a cenai..n.rabie partion of the light in one direction.
On this account, another form of the lamp is esed in houses. The oil vessel is a small globt, and the wick rises out of a nozzle formed on the t pper side of it. The only objection to this is, that the sin lace of the oil sinks down as it is consumed, and at length the wick has to draw the oil tip front such a depth, that it can only yield a diralinisla ed supply to the flame.
The lountain reservoir is a very good method of supply ing the wick °fa lamp with oil : See Plate CCCXL11. 11. In this, the reservoir AA, which contains the store of oil, has only one opening in it, and that is in a neck B pro ceeding from the lowest part. The reservoir must be in verted in order to fill it with oil ; but when it is in use, the opening into the neck is immersed beneath the surface of the oil contained in the small cup or dish D. Where the Wick C is placed, the oil in the cup D precludes the ad mission of air, and consequently the oil cannot descend out cif the reservoir. But when the oil in the cup D is so far diminished, as to allow a bubble of air to enter into the opening of the neck B, it will rise up into the reservoir, and allow an equal quantity of oil to descend into the cup for the supply of the wick. But as this will raise the oil in the cup, so as to cover the opening into tile neck, no more oil can come out until that which is in the cup is consumed. By this means, as long as the reservoir contains oil, the oil in the cup must always preset ve the same level, but will never run over. E represents the small nozzle, which holds up the wick in a perpendicular direction. It is a short piece of tube, with three projecting feet at the lower part, which stand in the bottom of the cup.
The fountain reservoir was known by the name of the of Cordon in the time of Mt. Boyle. That gentleman made one in an improved form, which is described in the early Philosophical Transactions. It consists only in mak ing the cup D, into w inch the oil descends, of a considera ble area, and forming a communication between this and another small cup, which receives the wick. By this means, the oil is less liable to descend in gluts.
Fig. 10. is a simple lamp, which has the property of sup plying the wick very regularly with oil. This is called the automaton lamp ; and a Mr. Porter had a patent for it in 1804. The wick is situated at f, at one end of a rectan gular vessel AA, which contains the oil. The whole lamp is suspended by a wire loop R on centre-pins at k, in the manner of a scale beam, so that the lamp is at liberty to Ii 'irate freely. The position of the centre k is such, that the lamp will incline as the oil contained in it diminishes, as shcwn by thc dotted lines ; and the inclination will in all cases be such, that the surface of the oil will just reach to toe proper height on the wick. The makers of these
lamps have attained this end from experiment with great precision, and the drawing, Fig. 10. is taken from one of then.
The best kind of lamp is that of Argand, which was in vented in France about 1784. The wick is a hollow cy linder or tube ; and the upper part of it when lighted, forms a t mg or short tube of flame. A rapid current of air is made to pass through the inside of the tube as well as othaioe. To produce this current, a cylindrical glass nbiinney is placed over the flame, and the rarified air which ascends the chimney, causes a current to pass on each side of the flame, that is, on the outside and inside of the ring of liarne, This lamp is exhibited in Plate CCCXLII. Figs. 1 and 2, the funnel representing the external form, and Fig. 2, a section of the part called the burner, which contains the wick. A, Fig. I, is the oil reservoir, from which the oil c.c.s:tends into the oil cistern B, one drop at a time, and is thence conveyed by a pipe C to the burner E. The exter nal appearance of the burner IS a pet vindicular tube, E ; within this is a smaller tube (Fig. 2.) which is closely united to the former at the lower end, but both are open at top. space between the two tubes. therefore, fords a narrow ciecular cistern, which is freely supplied with oil through the pipe C, but the oil cannot rise above the dotted line e, becate the oil reservoir A is consti acted in the manner of tffe fountain. The wick G is a circular tube of cotton, placed in the space between toe two tubes E and F, and the top or u•per end of the cotton rises a nide above the tubes at f. At that part the flame is His the glass chimaey, which rt=es up to a considerable height, as shown in Fig. 1. ; the lowt r part is enlarged, and sn nds on a small circular gallery I I. "The interior tube F, 2. is open at thc lower cod, and the air can freely cuter therein as shewit by the arrows ; and this air rising up thianigh the tuhe F, innat p•ss in contact with the interior of the circular ring of llama. The air for the supply of the external part of the flame enters beneath the gallery I I, and rises up within the glass chimney, which is contracted at the place most favourable fur projecting the air upon the flame. This chimney is one of the great improvem,_nts in troduced by M. Argand: The heated air in the glass chim ney, being lighter than the external air, is forced upwards by the cold air which rushes in beneath the edge of the glass chimney, and also up the interior tube as shcwn by the arrows. This Geld air passing in immediate contact with the flame affords oxygen 0 it ; and that portion of air which is not consumed becomes heated, and, by ascending the chimney, gives place to a fresh suppiy of air, SQ that a constant current is kept up.