A statical lamp for the same purpose is slse.wn in Fig. 4. It was invented by M. Edelcrantz. This is on the nie principle as Mr. Keir's, except that the maintaining- power to raise up flic oil is the weig it of the lamp itse.f, or rather the weight of the upper part of it. The oil reservoir is at AA, and is capable of enlarging and diminishing its dimen sions. The bottom of the pedestal is a cylindrical vessel LL, which is open at top, and within it is a hollow cylinder n, closed at the top ; the two cylinders arc closely joined together at bottom, and form a narrow circular space L n between the two; this space is filled with mercury. 1 he real oil vessel AA is open at the bottom, and the lower edge of it is immersed in the mercury I, a, so that the oil cannot escape. A tube a b rises from the oil vessel up to the burner E, which is made the same as in Fig. 2• Now the oil vessel AA, and the burner E, being filled with oil as high as the dotted line DD, it will not be able to escape, because the lower edge of the vessel is immersed in the mercury contained in the circular space a n, but the oil will press on the upper surface of the oil vessel AA with a levee propor tional to the altitude of the column ; and to resist this the vessel must be loaded with weights, x x, in addition to the weight of the burner and superstructure. As the oil (limit, ishcs, the oil vessel and the upper part of the lamp will descend, and diminish the capacity of the oil vessel A as much as the oil has lost by burning ; because the weight being constantly the same, it will always require a column of the same altitude to keep it in equilibrium, viz. from Ito D. Hence in this lamp, though the oil does not stand al ways at the same level, yet the lamp sinks as much as the oil wastes, so that it is always at the same height below the flame. R is a wire fixed perpendicularly, to guide and steady the lamp when it rises or falls.
Mr. 13arton's hydrostatic lamp is on the same principle as that of Mr. Edelerantz, but is more complete, because it is not so liable to be deranged by a small difference of the load. In Air. Barton's the external vessel L is carried upwards to a sufficient height to employ water instead of mercury ; this will he when the water is as high as the, dotted line KK, and it is evident that the effect will then be the same as before described.
Mr. Barton does not employ the Argand burner, but 4 burners with wicks the size of that of a candle.
The lamp which we consider the most perfect for the eloset of a student, is the mechanical lamp of Carcel. In this the burner is upon Argand's construction, and the oil is always supplied to it by small double pumps worked by a piece of mechanism in the lower part of the pedestal. The advantage of this lamp is, that the oil can always be sup plied in abundance without ever rising too high or sinking too low ; the pumps are adapted to raise more oil than the flame consumes, and the superfluity runs over the top of the tube containing the wick, and runs down to the pumps again.
Fig. 5. is a view of this lamp, and a section of the part containing the mechanism for the pumps. AA is the oil vessel ; B the pumps from which the oil is carried up by a pipeX to the burner at the top of the pedestal. The me chanism which gives motion to the pumps is contained in the space beneath the oil vessel A ; the maintaining power is a clock-spring D, which must he wound up every day by a key like a watch. On the lower edge of the barrel is a cog wheel of 108 teeth ; this turns a pinion of 12 leaves on the arbor of a second wheel which has 84 teeth, and turns amnion of 12 on the arbor of a wheel of 96 ; this turns a pinion of 12, on the arbor of which is a small crank to give motion to the pumps B ; on the same arbor is a wheel which turns a worm, and a fly or fan, to regulate the mo tion. To convey the motion to the pumps B, which are in the upper chamber or oil vessel, a small arbor rises perpen dicularly up through the bottom of the oil vessel. This ar bor has a lever on the lower end which the crank actuates, and on the upper end a double lever with two arms turning down to work the two pump pistons; the arbor of the lever passes through a tube joined to the bottom of the oil vessel, and a small glass is cemented round the tube to contain a few drops of treacle, which is viscid, and will not suffer the oil to leak down by the arbor into the wheel-work.
Figs. 6 and 7 represent the double pump. It has two barrels or chambers, with a piston working in each. The pistons a b are only small pieces of steel wire, and the cham bers or barrels are holes drilled horizontally in a thick piece of brass 13, the wires are accurately fitted to these holes, and require no packing. The valves of the pumps are shewn in Fig. 7 ; Sand for the convenience of repairing then), they are situated in the joints between the piece of brass B, which receives the pistons, and two others, plate E and F, one above and the other below ; the ascending pipe C is soldered to the upper piece, and all three are firmly joined together by a screw at each angle.
These lamps are in great use in Paris ; and we have found them answer their intended purpose better than any of the others which we have tried.
Street Lamps. The common lamps for illuminating the streets of London, are upon a very imperfect construction, being only a flat oil dish for a bunter, suspended in a glass vase. No provision is made for the entrance of the fresh air, except through the same chimney at which the smoke and heated air issue. From the defective supply of air. the flame is very weak, and the glass is soon obscured by the smoke. To increase the light, some parishes in London have adopted lamps with lenses, to concentrate the light, and throw it upon particular parts of the foot-path ; but as this must abstract the light from ot bet parts of the space which should be illuminated, no advantage whatever is gain ed by this addition.