416 SAFETY LAMP. 



figure, hydrogen, either pure or carburetted, be allowed, by means 

 of the pipe, to enter the glass cylinder, so as to form with the air in 

 it an explosive mixture, there will, nevertheless, be no explosion. It 

 will be found that as the quantity of inflammable gas increases, the 

 flame of the lamp enlarges, until it reaches the wire gauze, where it 

 burns more or less actively, according as the supply of atmospheric 

 air is greater or less. It will, under these circumstances, often ap- 

 pear as if the combustion had ceased, but on increasing the propor- 

 tion of atmospheric air, the flame will gradually contract, and finally 

 settle upon the wick, which will burn as at first, when the supply of 

 hydrogen ceases." 



"If the cage be removed from the lamp, and the experiment repeat- 

 ed in all other respects as at first, an explosion will ensue, as soon as 

 a sufficient quantity of hydrogen is allowed to enter the cylinder." 



It appears that Mr. Stevenson invented a lamp, whose light was 

 enclosed in a lantern, to which air was admitted by a number of 

 tubes, and any explosion within did not communicate to the air with- 

 out. 



The principal inconveniences of Sir H. Davy's lamp are, its lia- 

 bility to injury, on account of its delicate texture, and if there is a hole 

 made in it, the explosive atmosphere without may be readily fired ; it 

 is evident also that it does not afford a strong light, and the work- 

 men are sometimes tempted if possible, to open it, even in dangerous 

 situations, and accidents are said to have occurred from that cause. 

 Dr. Murray invented a safety lamp, of which an account is given by 

 his son,* founded upon the well known fact, that the inflammable 

 gas occupies principally the upper cavities, and that the air on the 

 floor is ordinarily good. The air for the support of the flame is 

 drawn from the floor, by a flexible tube, passing from the bottom of 

 the lamp, while the chimney at the top, by the strong current which 

 it is constantly discharging, prevents the entrance of gas from that 

 direction. The lamp is also of sufficient strength, and being furnish- 

 ed with a good mirror and lens, it throws a strong light, and it is 

 said that if an explosion should happen in it, it would merely extin- 

 guish the light, but would not extend to the atmosphere without. f 



* Elements, 6th Ed. Vol. I, p. 609. 



t Trans. Roy. 8oc. Edin. Vol. VI, p, 31. 



