414 SAFETY LAMP. 



raising and trimming the wick, and recruiting the oil, without open- 

 ing the lamp in the explosive atmosphere. 



0*0 When the proportion of the fire damp in the air is T ' the 

 wick of the lamp is seen surrounded by a faint blue flame. 



(k.) When the proportion is increased to |, j, or j, the lantern 

 is filled with the flame, burning green, as I have observed it in labo- 

 tory experiments ; still, the flame, even when the wire is red hot, 

 does not communicate to the exterior air, although it should be in an 

 explosive state.* 



(I.) Should danger arise from a current of explosive gas passing 

 through so rapidly as to heat the wire to such a degree that it might 

 inflame the air ; still the increase of the cooling surface, either by di- 

 minishing the size or increasing the number of the apertures, would 

 obviate the danger, for the safety of the instrument is supposed to 

 consist in the cooling powers of the wire, reducing the explosive 

 gas below that temperature at which it is inflammable, which tem- 

 perature is stated to be far above a white heat.f 



(m.) Even when the- noxious gases prevail, so as to extinguish 

 the lamp, and thus threaten life by suffocation, a small coil of plati- 

 num wire, hung above the lamp, within the wire gauze cylinder, will 

 continue to glow, and will enable the miner to grope his way through 

 regions otherwise perfectly dark. This combustion is owing to the fire 

 damp, but it does not communicate to the external air ; and on com- 

 ing into better air, the lamp will frequently be rekindled spontaneously. 



* The miner should, however, then withdraw, because the wire may be so rapidly 

 oxidized as to fall to pieces, and he may be in danger also of suffocation, from the 

 prevalence of irrespirable gases. 



t Sir H. Davy's theory of the safety lamp is called in question by M. G. Sibri, 

 (Bib. Univ. Mars, 1827, and Am. Jour. Vol. XIII, p. 179.) who contends that it is 

 not owing to the cooling power of the metal, but to a repulsion existing between 

 flame, and any substance that may be brought near it. It is repelled equally by a 

 rod of glass or porcelain, as by one of metal, and the effect depends not on the nature 

 of the body, but is proportioned directly to its bulk, and inversely to its distance ; 

 even two flames will repel each other, and so gross a flame as that of a candle, will 

 refuse to pass between two rods of any kind, (even wood,) brought near to each other 

 on opposite sides of the flame, and near the summit. The repulsion is not all affect- 

 ed by the temperature of the substance. I have repeated these experiments, and 

 find them exact, and the cause is obvious ; the repulsion appears to be occasioned by 

 the gas, which is incessantly blowing out from flame, and which striking against any 

 obstacle, reacts, to inflect the flame ; just as a current of lava will sometimes stop 

 short, at a wall, rise parallel to, and finally cascade over it, without touching it ; this 

 well ascertaained fact is owing to the great quantity of ae'rial matter blown out by 

 lava, and which, meeting with an obstacle, reacts upon it as above described, with 

 respect to flame. Mr. Sibri conceives that the number of wires in the metallic 

 gauze of the safety lamp, is by far too great, and that the same security would be af- 

 forded by such a number as would merely give strengh to the instrument, without 

 so much impeding the light. I have never felt satisfied with this part of the theory 

 of the safety lamp, given by its illustrious inventor, and am disposed to think that 

 the one suggested above is the principal source of protection ; in this opinion I am 

 supported by Prof. J. Griscom, to whom I am indebted for the notice of Mr. Sibris' 



