240 Sir Frederick Ahel [March 13, 



will be increased by the user of the lamp, and as the evaporation of 

 the oil will take place more slowly from each portion of the wick 

 which furnishes the flame, the heat to which the cotton is exposed 

 will be greater, and the charring, which is fatal to the jDroper feeding 

 of the flame by destroying the porosity of the end of the wick, will 

 take place more rapidly and to a mucli greater extent. 



Even with wicks of the higher qualities, considerable differences 

 exist in the rapidity with which the oil is raised to the flame. In Mr. 

 Eedwood's experiments, conducted with a specimen of English wick 

 of good quality and with a very superior American wick, of corre- 

 sponding dimensions, the quantity of oil sijDhoned over by the latter 

 in a given time, was from 35 to 47 per cent, greater (according to the 

 nature of oil experimented with) than that carried over by the English 

 wick. 



If the wick be at all damp when taken into use, its power of 

 conveying the oil to the flame will be decidedly diminished, the 

 capillaries of the fibre being more or less filled with moisture, and 

 similarly, if the oil accidentally contain any water, the latter, passing 

 into the wick, will interfere with the j)roper feeding of the flame. As 

 the oil is very thoroughly filtered or strained during its transmission 

 through the body of the wick to the flame, it is obvious that any 

 impurities suspended in the liquid will be deposited within the wick 

 and will gradually diminish its porosity. For this reason the same 

 wick should not be used for a great length of time, and it is decidedly 

 objectionable to use a much greater length of wick than is necessary 

 to reach to the bottom of the reservoir, and to continue its use until 

 it has become too greatly shortened by sucessive trimmings. On the 

 other hand, the wick should always be of sufficient length to be 

 immersed to a considerable distance in the oil. It is evident that 

 the copious supj^ly of oil to the flame will become reduced as the 

 column of liquid which covers the wick in the reservoir becomes 

 reduced in height ; hence the supply of oil in the lamp should never 

 be allowed to get very low, not only because it is undesirable to have 

 a large air-space which may be filled with vapour and air, but also 

 because the burning of the lamp is injuriously affected thereby. 



Some lamj)s, of patterns first constructed in the United States, are 

 provided with what may be called a feeding wick in addition to the 

 wick, or wicks, which furnish the flame. This wick is generally 

 simply suspended from the lower surface of the burner, and reaches 

 nearly to the bottom of the reservoir, being so placed that it hangs 

 against one flat side of the regular wick, and thus aids considerably 

 the copious and uniform absorption of oil by the latter. In certain 

 lamps of recent construction the reservoir which contains the main 

 supply of oil is so arranged (upon the principle of the old study- 

 or Queen's oil-lamp), that it regularly maintains at a uniform level 

 the supply of oil, which surrounds the wick in a small central reser- 

 voir or cylinder, separated from the main reservoir (excepting as 

 regards a small channel of communication) by an air-space, which 



