LAMP. 



507 



t*j|P- notch in the side of the tube, which turn^ the ring, al- 



lows it to rise or fall without communicating a similar 



1 1 motion to that tube or gallery. R is a shade which 



-'i> I, 2. surrounds the light and prevents it? action on the eyes. 



This is particularly useful for reading or writing, as it 



also reflects the light upon the paper. 



The construction of the fountain reservoir for the 

 Argarul lamp, is also explained in Fig. '2. The oil re- 

 servoir A terminate* at the lower end with a neck 

 which screws into the oil cistern B. A hole H made in 

 the neck at one side for the oil to come out ; but this 

 cannot happen until the surface of the oil in the cistern 

 B is drawn down below the dotted line, so as to admit 

 air to enter the opening, and then a drop of oil comes 

 down. The air has free admission into the cistern B 

 through a hole i. When the lamp is extinguished, the 

 small knob or handle I is drawn up, which closes the 

 hole H by the short tube o sliding over it, and prevents 

 the oil from being spilt if the lamp is inclined. 



The fountain reservoir casts a very extensive shadow, 

 and u therefore best adapted to be placed against a wall. 

 It i- a great advantage- in lamps to have the oil reser- 

 voir situated beneath the burner, so that the light will 

 not be intercepted in any direction ; and there are se- 

 veral ingenious methods of railing up the oil to a con- 

 stant level for the supply of the wick. 



t)r. Hook's semicylindrical counterpoise, described 

 in our article HYDRODI x v :: -. Vol. xi. p. 48*, was in- 

 tended to retain toe oil of a lamp always at a constant 

 height. 



lMr*i' . I he hydropneumatic lamp is a small Hungarian ma- 

 jpaucltoip. chine or Chemnitz fountain; see our article HVDHO- 

 NAMICS Vol. xi. p. ,(.-. The pedestal of the lamp con- 

 tains three oil cisterns, one above the other. The upper 

 cistern is at the top of the pedestal, immediately be- 

 neath the burner or wick holder, and is made air tight ; 

 it has a pipe i smutting from the bottom of it to fee<l the 

 burner with ml ; this is therefore the oil reser\ oir. The 

 second cistern w placed beneath the former, and is open 

 to toe external air ; a pipe descends front it to the bot- 

 tom of the third or lower cistern. The latter is nude 

 impervious to air, and has a pipe ascending from the 

 top of it to the top of the upper vessel or reservoir. 



nose the two upper cisterns to be full of oil, and 

 the lower one empty ; the oil in the second cistern being 

 preaitd upon by the air, the oil in it descends through 

 the pipe to the bottom cistern, and enter* therein ; but 

 as the contained air cannot escape from this vevwl ex- 

 through the air pipe to the upper vesael or reser- 

 voir : it ascend* tin rein, and presses upon the surface of 

 the oil so u to force it up the pipe, to the burner which 

 is constructed, on Argand's plan, as in Fig. . The 

 height to which the oil will ri*e in the space between 

 the two tubes EF of the burner, it regulated by the 

 height of the middle cistern above the lowe-t, because 

 the pressure of that column of fluid is transferred by 

 the medium of the air to elevate the oil out of the top 

 Cittern into the burner. 



When all the oil in the second cistern has descended 

 to the lower cistern, the power of action will be ex- 

 hansted, and must be renovated by inverting the whol 

 lamp, and then the oil from the bottom cistern runs 

 back, and the oil reservoir being again filled, the lamp 

 * fMD ready to proceed. In lamp* for common use 

 the reservoir is made sufficiently capacious for tl . 

 of one night ; but tliry nave been mu 

 staircases of a sufficient size to hold oil fur a 



This lamp is called the French lamp, because tli? 



were first brought from France. But we have seen a Lamp, 

 letter from Mr. Watt to M. Argand, dated 1787, sug- ^ "V^ 

 gesting this plan in a form very little different from 

 what is at present used ; and in consequence of this, 

 M. Argand first made them in France. 



We have lately found a figure of such a lamp in an 

 Italian work, entitled Le Machine, by Branca of Rome, 

 published in 1629. 



The hydrostatic lamp, first described by Dr. St. Claire St. Claire's 

 in the Philosophical Transactions, and afterwards im- ,/^ ros ^" c 

 proved by Mr. Keir, is shewn in section in Fig. 3. FF pf^'d by 

 is the burner where the wick G is placed. This may Keir. 

 be constructed upon Argand's plan, as we have already PLATE 

 described, but the figure represents a flat wick G, with CCCXLH. 

 a rack and pinion for elevating and regulating its height & 

 above the nozzle. The oil reservoir is situated in the 

 bottom of the pedestal at A, and is closed on all sides 

 except where a pipe a b ascends to the burner E ; and 

 also another pipe, which communicates with a small cis- 

 tern It The latter is open to the atmosphere, and is fill- 

 ed with a solution of salt and water, which fluid being 

 of greater specific gravity tlian the oil, a column of it, 

 which is equal in altitude to AB, will sustain a higher 

 column of oil, via-, from A to the dotted line F, which 

 is the level at which the oil will stand m the burner. 

 The proportion of the column of water to that of the 

 oil is generally as three to four. As the oil is diminished 

 by burning, the height of the column of oil will be di- 

 minished, and will no longer balance the column of 

 water, which will therefore descend ; but on entering 

 into the vessel A it will displace the oil from it, and 

 before the two come again t<> an equilibrium, the water 

 will have restored to the oil column three-fourths of 

 that height which it had lost by waste. As this loss of 

 weight is to be reckoned on the surface of the large re- 

 servoir A, it is very slow ; and from the above con- 

 trivance, the height of oil only partakes of one-fourth 

 of it. Therefore the height of the oil in the burner is 

 kept sufficiently constant to supply the flame very re- 

 gularly. 



A statical lamp for the :ame purpose is shewn in Fig. E,| C I. 

 4. It was invented by M. Edelcrantz. This is on the crantzV 

 same principle as Mr. Keir's, except that the maintain- statical 

 ing power to raise up the oil is the weight of the lamp 'p. ml> ', 

 it-rlt, or rather the weight of the upper part of it. The lg- ' 

 oil reservoir is at AA, and is capable of enlarging and 

 diminishing its dimension". The lx>ttom of the pedestal 

 it cylindrical vessel I.I,, which i< open at top, and 

 within it is a hollow cylinder n u closed at the top; the 

 two cylinders are cloudy joined together at bottom, and 

 form n narrow circular space L n Iwtween the two ; this 

 space is fillc-.l with mercury. Tin- real oil vessel AA is 

 opm at the bottom, and the lower edge of it is im- 

 mersed in the mercury L n, so that the oil cannot es- 

 cape. 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 vetkel AA, and the burner E being filled with oil as 

 high as the dotted line IM), it will not be able to es- 

 cape, because the lower edge of the vessel is immersed 

 in the mercury contained in the circular space n n, but 

 the oil will press on the upper surface of the oil vessel 

 AA with a force proportional to the altitude of the co- 

 lumn ; and to re-i-t thi*the vessel must be loaded with 

 weights .r .r, in addition to the weight of the burner and 

 superstructure. As the oil diminishes, the oil vessel 

 and the upper part of the lamp will descend and dimi- 

 nish the capacity of the oil vessel A as much as the oil 

 ha* lo-t by burning; because the weight being constantly 

 the same, it will always require column of the same 



