276 



ARTIFICIAL LIGHTING 



long as the candle lasts. The heat of the burning wick melts ! 

 the fatty substance near it, and this liquid fat is quickly sucked ! 

 up into the burning wick. The heat of the flaming wick is 

 sufficient to change most of this liquid into a gas, that is, to 

 vaporize the liquid ; and to set fire to the gas thus formed. 

 These heated gases burn with a bright yellow flame. 



Small particles of carbon are also set free from the unvaporized 

 fatty liquid, and these, on coming in contact with the oxygen 

 of the surrounding air, glow with an intense heat and increase 

 the brightness of the candle flame. 



The oil lamp. The simple candle of our ancestors was 

 later replaced by the oil lamp which gives a brighter, steadier, 



and more permanent illu- 

 mination (Fig. 140). The 

 principle of the lamp is 

 similar to that of the can- 

 dle, except that the wick 

 is saturated with kerosene : 

 or oil rather than with fat. | 

 The heat from the burning 

 wick is sufficient to change \ 

 the oil into a gas and then ^ 

 to set fire to the gas. By ; 

 placing a lamp chimney 

 over the burning wick, a : 

 constant and uniform draft ( 

 of air is secured around the 

 blazing gases, and hence a I 

 steady, unflickering light is obtained. If the quantity of air : 

 which enters at the bottom of the chimney is insufficient, some i 

 of the carbon particles are not burned and form soot. A lamp 

 " smokes " when the air which reaches the wick is insufficient i 

 to burn to incandescence the rapidly formed carbon particles; 



FIG. 140. The oil lamp. 



