236 THE FARMER AT HOME. 



slowly, long journeys in countries impassable to most other animals, 

 and are much employed in transporting the rich ores, dug out of the 

 mines of Potosi, over the rugged hills arid narrow paths of the Andes. 

 They lie down to be loaded, and, when weary, no blows can excite 

 them to quicken their pace. They neither defend themselves with 

 their feet nor teeth ; when angry, they have no other method of 

 avenging injuries but by spitting. They can throw out their saliva 

 to the distance of ten paces ; and if it fall on the skin it raises an 

 itching, accompanied with a slight inflammation. 



LAMP. A well known apparatus for producing artificial light. 

 A lamp in the most simple form, has a wick, composed of several 

 cotton threads, partially immersed in oil, contained in a flat dish, 

 furnished with some small support, to hold the upper end of the wick 

 in a perpendicular direction, a small height above the surface of the 

 oil ; this oil holder, or dish, when suspended in a globular glass case, 

 is the common street lamp. When the wick is lighted, by the appli- 

 cation of a burning torch, the heat of its flame causes the oil, which 

 is contained in the wick, to boil, or rise in vapor ; and the combustion 

 of this vapor is the flame which produces the light. As fast as the 

 oil in the wick is carried offj by this evaporation, a fresh supply is 

 drawn up, by the capillary attraction of the wick, from the oil con- 

 tained in the oil-holder. 



Hence, it appears that lamps and candles are both of the same 

 nature as gas-lights. The difference consists in the materials from 

 which the gas is extracted, and the manner in which the extracting 

 of it is performed ; but in all cases, flame is nothing more than the 

 combustion of gas. In gas-lights, an apparatus is previously employed, 

 to make and preserve the gas, and to conduct it to the place where 

 artificial light is to be obtained from its combustion ; but in lamps 

 and candles, the heat of the same flame which produces the light, is 

 employed to vaporize the combustible matter, and form gas for its 

 own maintenance. The difference between lamps and candles is, that 

 lamps are supplied with the combustible matter in a fluid state, but 

 candles are supplied with a solid material ; and the heat of the flame 

 must first be employed, to reduce the tallow or wax to a fluid state ; 

 and this fluid, which forms itself round the base of this wick, sustains 

 the flame just in the same manner as the oil in lamps. 



The flame which we employ for artificial light, is produced by the 

 combustion of some gas which contains carbonaceous matter ; and 

 it is most probable that the matter, while it burns in these gases, is 

 chiefly composed of particles of carbon in a very minute state of division. 

 Combustion takes place when the carbon combines with the oxygen of 

 the atmospheric air, in the requisite proportion to produce the carbonic 

 acid gas ; and if the oxygen is supplied in a less proportion, the oxide 

 of carbon will be produced in the form of smoke or soot. The chief 

 circumstance influencing the combustion of the different carbonaceous 



