Burning Gas for the purpose of Illumination. 299 



tion to be taken with them, is to take care not to raise them 

 so high as to smoke, and never to use two or more low flames, 

 when the same degree of light can be got from one flame 

 burning at its most effective height. 



A mode of supplying argand burners with a current of heat- 

 ed air has been lately proposed in Paris, and much praised in 

 London. This is effected by having an outer glass of a dia- 

 meter a little larger than the inner one. This outer glass 

 reaches farther down than the bottom of the burner, and is 

 closed below by a metal plate ; the air for the supply of the 

 flame is made to pass down between the outer and inner 

 glasses, where it gets heated ; it then enters the inner glass and 

 the centre aperture of the bm-ner, and passing upwards, sup- 

 ports the combustion of the gas in the usual way. There is no 

 doubt that, by this arrangement, a considerable improvement 

 may be made in cases where ill made burners, with wide and tall 

 chimney-glasses are employed; but if the experiment be tried 

 with burners and glasses proportioned in the way recommended 

 above, it will be found that no advantage is gained, and that 

 the maximum eflPect has been attained by a simpler apparatus. 



Before quitting the subject of burners, it may be right to 

 advert to a frequent cause of disappointment in their perform- 

 ance. The perfection of an argand burner is, that the flame 

 arising from it should appear in a continuous cylindric sheet, 

 with a smooth upper edge, and without forking points. This is 

 sometimes very difficult of attainment, however carefully the 

 jet-holes may be gauged by the pricker. There are two causes 

 for this irregularity ; one is, that, if the drill which is used be 

 blunt, a Uttle blaze is pushed aside by it when it is forced 

 through the plate in which the jet-holes are pierced ; this 

 blaze adheres to the edges of the hole, and interferes with the 

 passage of the gas, and. being unequal in its effects, renders the 

 flame forked. The other cause is, that the inside of the bm-ner 

 is seldom turned true, and that the shoulder in which the 

 pierced disk rests, is not of equal width all round, and some- 

 times may be so thick in some places, that the drill, when it 

 gets through the disk, strikes against the shoulder ; this like- 

 wise interferes with the issue of the gas. To avoid these 

 causes of irregularity, the following precautions are essential. 



