LAMP. 



357 



iii the fullest degree, to produce the greatest quantity 

 ol flame without any smoke. 



To make a lamp burn with a clear and steady 

 light, the length of wick standing up above the 

 tube or nozzle, which supports the wick, must be 

 regulated according to its capacity for conducting 

 the oil, otherwise the whole of the oil which it sup- 

 plies will be volatilized by that portion of flame which 

 surrounds the lower part of the wick. In this case, 

 the upper part of the wick, which is in the centre of 

 the flame, will burn to a charcoal or snuff. 



A snuff in the centre of the flame, produces a smoke, 

 and a great diminution of light, which it occasions, 

 by increasing the body of the wick ; and as the air 

 cannot have free access to the wick in the centre of 

 the flame, the gas there produced cannot burn im- 

 mediately, but must i ise upwards, and will inflame 

 when it gets high enough to meet the air, provided 

 it then retains a sufficient heat. This ascent of the 

 vapour before it inflames, is the cause of the pyra- 

 midal form of the flame ; the vapour arising from the 

 central parts of the wick being obliged to rise to a 

 greater height before it can meet with sufficient 

 oxygen to burn. On the other hand, a wick, which 

 is too little raised above the nozzle will not volatilize 

 the oil so fast as it draws it up ; still what is volatilized 

 is perfectly burned, and smoke is not produced. 



A torch is composed of the resinous part of fir or 

 pine, and the turpentine, or melted rosin, oozes 

 through the pores of the wood to the flame, in a slow 

 and regular manner, producing a dull light. The 

 candle is an improvement upon the torch, and con- 

 sists, as every one knows, of a few threads of cotton 

 or other fibrous substance called a wick, enveloped 

 in a cylinder of tallow or wax. Flame being com- 

 municated to the wick, combustion begins, and the 

 radiated heat melts the tallow nearest to the wick, 

 and it ascends to the flame through the wick by 

 capillary action, being converted into gas so soon 

 as it reaches the surface, which gas enters into 

 combustion, and a bright flame is the consequence. 

 A common lamp acts on the same principle, but the 

 combustible employed being a liquid, a vessel is 

 necessary to contain it. The common liquid em- 

 ployed in this country is whale oil, on the continent 

 oil of poppies, nuts, rape seed, and the inferior kinds 

 of olive oil, are used. Naphtha is also used. In 

 some cases the vessel is open at top, and the wick 

 projects from a sort of beak in the side ; but the usual 

 plan now is to close the top of the vessel with a 

 cover, and lead the wick up through a hole in the 

 middle ; but here a small opening must be left, to 

 admit the pressure of the air, so that the oil may rise 

 in the wick. In this latter construction, if the vessel 

 be large, a dark broad shadow will be thrown below 

 the lamp, and much light lost. To avoid this, lamps 

 have been made with the vessel or reservoir contain- 

 ing the oil, placed at a considerable distance from the 

 burner. Among contrivances of this nature, the 

 Astral or Sinumbral lamps, invented by count Rum- 

 ford, are the most esteemed. In count Rumford's 

 lamp, the oil is contained in a hollow circular ring, 

 the oil being led to the burner, which is in the cen- 

 tre, by means of radiating tubes. The ring is placed 

 somewhat below the level of the flame, and a small 

 hole is made in the upper surface for the admission 

 of air. The supply of oil has sometimes been effected 

 upon the principle of Hero's fountain. In this lamp, 

 oil is placed in a vessel having a tube leading down- 

 wards for some distance, then turning up a little it 

 enters another vessel. A syphon rises from the top 

 of this second vessel, and enters a third vessel higher 

 than the first, from which third vessel an inverted 

 syphon is led up to the burner. Oil is put into the 

 first, and falls gradually down into the second, and 



oil is placed in the third, there being a column of 

 air between the second and third vessels. As the 

 oil from the third vessel becomes exhausted, the 

 column of oil from the first vessel presses upon the 

 column of air communicating with the second and 

 third vessels, and thus raises the oil to supply the 

 burner. Other lamps are constructed so as to keep 

 the surface of the oil at one level, by placing it in 

 one leg of an inverted syphon, and balancing it with 

 some heavier fluid, such as salt water, in the other 

 leg. 



In France, the oil is kept at the proper level by 

 pumping the oil up, either occasionally by the hand, 

 or by clock work ; a clumsy contrivance. This is 

 much better accomplished in the simple and ingenious 

 lamp of Mr Porter. In this lamp the oil is contained 

 in an oblong box, having the wick tubes at one end, 

 and being suspended on an axis, nearer the wick end 

 than the other, so that when it is full, the additional 

 quantity of oil at the longer end will just balance the 

 additional weight of the wick tubes. It is clear that 

 as the oil is burned away, the wick end of the box 

 will fall, and the oil rise to the burner. 



Fountain lamps are constructed on the same prin- 

 ciple as the bird fountain used in cages. The large 

 reservoir is open at the bottom, a tube being placed 

 there at one side. This tube is immersed at the 

 outer extremity, in a small cavity containing oil, 

 nearly on a level with the burner. Whenever the 

 oil in the cavity falls under the level of the top of 

 the tube, a bubble of air enters, and rising to the 

 top of the reservoir, presses down more oil to the 

 cavity, and thus the wick is constantly supplied. 



A very simple kind of lamp is used to burn all 

 night in sick chambers : a small quantity of water 

 is poured into a glass tumbler, and above that a 

 quantity of oil. A bit of cork is now pierced, so 

 as to admit a few threads of cotton to pass through 

 it, and the cork being placed upon the oil will float, 

 the cotton threads will draw up the oil by capillary 

 action, and a feeble but clear light will be given. A 

 glass tube of small bore will answer instead of the 

 cotton threads. 



The great defect of common lamps is that the 

 wick being thick, the air can only come into con- 

 tact with a comparatively small portion of the 

 flame. This is in some measure rectified by spread- 

 ing out the wick so as to form a broad thin flame. 

 But the most important improvement in the form 

 of wicks and burners was made by M. Argand of 

 Geneva, in 1784. The annexed wood engraving is 

 a sectional view of Argand's lamp. A is the oil 



Fig. 1. 



