24 On Ike Article in our last Number, entitled 



quantities at a lime, will not explode, but be gradually consumed 

 by combustion — which is utterly false. Whatever quantity of 

 explosive gas is admitted to the contact of flame, it will explode, 

 that is, it will burn at once, and not be gradually consumed ; 

 and in the wire-gauze safe-lamp the whole cylinder is filled with 

 flame. 



But on this erroneous idea Mr. G. Stevenson, it is said, en- 

 deavoured to construct a safe-lamp : First, by admitting air by 

 one tube, then by three tubes (which Mr. R. Brandling calls ca- 

 pillary, though no dimensions are stated), and last of allj by a row 

 of small holes on the outside of a copper lamp covered with a cy- 

 linder of glass. This last is the only lamp which has been shown 

 in public. It is on this, therefore, that I shall make my obser- 

 vations. The holes in that which I saw were at least the l-r2th 

 of an inch in diameter below, and more than the l-6th of an 

 inch in diameter above, and therefore \Vould readily communi- 

 cate explosion : the glass cylinder was loose, and tliere was no- 

 thing to prevent the conmiunication of explosion through it. 

 I never heard that this lamp was exposed to any other proof 

 than that of sending pure fire-damp into it, which would extin- 

 guish the candle in a common lantern; or of being placed in 

 the upper part of a board, where the pure fire-damp immediately 

 extinguished it. It is certain that if an explosive mixture ever 

 began to burn in this apparatus, it must communicate explosion 

 to the outward atmos)jhere. I shall now say something of Sir 

 H.Davy's principles, which were made known to scientific men, 

 and pretty generally communicated, whilst Mr. G. Stevenson's 

 were in embryo, or confined to the Killingworth Colliery. 



Sir H. Davy's first idea of a safe-lamp was founded on a dis- 

 covery which he made — that a very small admixture of azote 

 prevented the explosion of detonating mixtures of fire-damp*. 

 Hence he made a light burn in a close lamp supplied with a 

 liuiited quantity of air; and when this air was further deteriorated 

 by an admixture of fire-damp the light was extinguished. This 

 lamp, though the principle of it was strictly philosophical, could 

 not have been very useful, for it must have been extinguished 

 by a very slight admixture of fire-damp in air. 



I must, however, vindicate this first principle of Sir H. Davy 

 against an enlightened and libera! advocate of his cause, the Rev. 

 John Hodgson, who says that Mr. John Murray thought of a 

 diminished atmosphere: whereas, as far as I can learn from 

 the perusal of his modest and luminous little treatise, he only 

 anticipated his namesake (Dr.jMurray) and Mr. R. W. Brandhng 

 in the idea of a tube for bringing the air from a distance. 



• See rhil. Mag. lor Dec. 1815, 



The 



