72 



Microscopical Essays. 



that the oil in the burner may return into the body when fo placed 

 and filled ; if, by being too full, any oil appears above the guard, 

 only move the lamp a little, and the oil will difappear ; the lamp 

 may then be placed erect, and the oil will flow to it's proper level. 



The oil muff be of the fpermaceti - kind, commonly called 

 chamber oil, which may generally be diftinguilhed by it's pale- 

 nefs, tranfparency, and inoffenfive fcent; all thofe oils which are 

 of a red and brown colour, and of an offenfive fcent, mould -be 

 carefully avoided, as their glutinous parts clog the lamp, and 

 the impurities in fuch oil not being inflammable, will accumulate 

 and remain in the form of a craft on the wick. Seal oil is nearly 

 as pale and fweet as chamber oil ; but being of a heavy fluggifh 

 quality, is not proper for lamps with fine wicks. 



Whenever bad oil has been ufed, on changing it, the wick muft 

 alfo be changed, becaufe. after having imbibed the coarfe par- 

 ticles in it's capillary tubes, it will not draw up the fine oil. 



To obtain the greater! degree of light, the wick fhould be trim- 

 med exaaiy even, the flame will then be completely equal. 



There will be a great advantage in keeping the lamp clean, 

 efpecially the burner and air tubes ; the negle6t of cleanlinefs in 

 lamps is too common : a candleftick is generally cleaned every 

 time it is ufed, fo fhould a lamp ; and if a candleftick is not to be 

 objetted to becaufe it does not give light after the candle is ex- 

 haufted, fo a lamp fhould not be thought ill of, if it does not 

 give light when it wants oil or cotton - but this laft has often hap- 

 pened, becaufe the deficiency is lefs vilible. 



