61 



not intercept an explosion from olefiant gas, would prevent it with 

 fire-damp. 



The combustibility of different gases is, to a certain extent, in 

 direct proportion to the masses of heated matter required to inflame 

 them. A red-hot wire, one fortieth of an inch in diameter, will not 

 ignite olefiant gas, but it will inflame hydrogen gas ; and the same 

 wire heated white-hot, will inflame olefiant gas, but will not inflame 

 the carburetted hydrogen of the coal-mines, which fortunately is the 

 least combustible of the inflammable gases. The cooling power of 

 metal, in regard to flame, is well shown by encircling a very small 

 flame with a cold iron wire, which instantly causes its extinction. 

 The interruption of the flame, therefore, in the author's safety-lamp, 

 depends upon no recondite cause, but is simply referable to the cool- 

 ing power of the wire-work tissue. 



From the facts contained in the first part of this paper, the author 

 conceives that the light of meteors depends not upon the ignition of 

 inflammable gases, but upon that of solid bodies ; that such is their 

 velocity of motion, as to excite sufficient heat for their ignition by 

 the compression even of rare air ; and that the phenomena of falling 

 stars may be explained by regarding them as small incombustible 

 bodies moving round the earth in very excentric orbits, and becoming 

 ignited only when they pass with immense rapidity through the 

 upper regions of the atmosphere ; while those meteors which throw 

 down stony bodies, are similarly circumstanced, combustible masses. 



Some new Experiments and Observations on the Combustion of gaseous 

 Mixtures ; with an Account of a Method of preserving a continued 

 Light in Mixtures of inflammable Gases and Air without Flame. By 

 Sir Humphry Davy, LL.D. F.R.S. V.P.R.I, Read January 23, 

 1817. \PhiL Trans. 1817, p. 77.] 



Having shown, in a former communication, that the temperature 

 of flame is considerably greater than that required for the ignition of 

 solid bodies, the author thought it probable that, during the com- 

 bination of certain gaseous substances, the heat evolved might be 

 adequate to the incandescence of solid matters exposed to them, 

 though insufficient to render the gases themselves luminous, or, in 

 other words, to produce flame. 



In a combustible mixture of coal-gas and air, the author suspended 

 a small wire-gauze safe-lamp, in which some fine platinum wire was 

 fixed above the flame ; and when the inflammation had taken place 

 within the cyh'nder of gauze, the quantity of coal-gas was increased, 

 under the idea that the heat acquired by the mixed gas in passing 

 through the wire gauze would prevent the excess from extinguishing 

 the flame. When this happened, the wire of platinum continued to 

 glow, though there was no inflamed gas in the cylinder ; so that the 

 oxygen and coal-gas in contact of the wire seemed to burn without 

 flame, and yet produced heat enough to keep the wire ignited. This 

 conclusion was verified by introducing a hot platinum wire into a 



