734 SAFETY LAMP 



the volume of tho air, the cylinder becomes filled with a feeble blue flame, while the 

 flame of the wick appears burning brightly within the blue flame. The light of the 

 wick augments till the fire-damp increases to |th or |th, when it is lost in the 

 flame of the fire-damp, which in this case fills the cylinder with a pretty strong light. 

 As long as any explosive mixture of gas exists in contact with the lamp, so long it 

 will give light ; and when it is extinguished, which happens whenever the foul air 

 constitutes so much as frd of the volume of the atmosphere, the air is no longer 

 proper for respiration ; for although animal life will continue where flame is extin- 

 guished, yet it is always with suffering. By fixing a coil of platinum-wire above the 

 wick, ignition may be continued in the metal when the lamp itself is extinguished ; 

 and from this ignited wire the wick may be ngain rekindled, on carrying it into a less 

 inflammable atmosphere. This arrangement, however, is rarely employed. 



The late Mr. John Buddie, one of the most experienced of coal-miners, wrote as 

 follows, in the 'Journal of Science,' on the general use of the safety-lamp : 'We have 

 frequently used the lamps where the explosive mixture was so high as to heat the 

 wire-gauze red-hot ; but on examining a lamp which has been in constant use for three 

 months, and occasionally subjected to this degree of heat, I cannot perceive that the 

 gauze-cylinder of iron-wire is at all impaired. I have not, however, thought it 

 prudent, in our present state of experience, to persist in using the lamps under such 

 circumstances, because I have observed, that in such situations the particles of coal- 

 dust floating in the air, fire at the gas burning within the cylinder, and fly off in small 

 luminous sparks. This appearance, I must confess, alarmed me in the first instance, 

 but experience soon proved that it was not dangerous. 



' Besides the facilities afforded by this invention to the working of coal-mines 

 abounding in fire-damp, it has enabled the directors and superintendents to ascertain, 

 with the utmost precision and expedition, both the presence, the quantity, and correct 

 situation of the gas. Instead of creeping inch by inch with a candle, as is usual, along 

 the galleries of a mine suspected to contain fire-damp, in order to ascertain its pre- 

 sence, we walk firmly on with the safety-lamp, and, with the utmost confidence, 

 prove the actual state of the mine. By observing attentively tho several appearances 

 upon the flame of the lamp, in an examination of this kind, the cause of accidents 

 which happened to the most experienced and cautious miners is completely deve- 

 loped ; and this has hitherto been in a great measure matter of mere conjecture.' 



The two first safety-lamps used in a colliery are preserved in the Museum of 

 Practical Geology. 



The action of the wire-gauze has been supposed to depend upon a cooling-process ; 

 but many experiments tried by the Editor of the present work tends to convince him 

 that the cooling hypothesis will not explain the phenomenon. He conceives the 

 impermeability of wire-gauze to flame to be due to a repulsive power established 

 between the hot metal and the ignited gas, similar in character, although differing in 

 condition, to that which prevails between water and a white-hot metal. 



George Stephenson, proceeding not improbably upon the data furnished by Mr. 

 Tennant, with that peculiar aptitude in mechanical design which ever characterised 

 that remarkable man, at once, and without any knowledge of the researches of the 

 chemist, devised a lamp by which air was admitted to the flame through ' apertures 

 of wire-gauze.' This lamp is said by Mr. Brandling to have been tried in ' the 

 Killingworth pits on Saturday, October 21, 1815.' The result, however, of a very 

 careful examination of the question as between George Stephenson and Humphry 

 Davy by a meeting of coal-owners, was, on October 11, 1816, a decision that 

 the merits of discovering a real safety-lamp belonged to Davy ; and on September 

 13, 1817, a service of plate was presented by the coal-owners at Newcastle, 'as 

 a testimony of their gratitude for the services you have rendered to them and to 

 humanity.' 



Numerous modifications of the Davy safety-lamp have been from time to time 

 introduced. A few of the more important must bo named : 



George Stephenson modified his original plan. His modified lamp consisted of 

 a wire-gauze cylinder about 2 j inches diameter, and about 6 inches high, with a 

 glass shield inside. The air for combustion was admitted through a series of per- 

 forations in the bottom, and a metal chimney, full of small holes, is fixed inside on 

 the top of the glass-cylinder. The ' Geordie,' as the Stephenson lamp is familiarly 

 called, has been much used in fiery collieries. 



Mr. Smith, of Newcastle, improved this by covering all the perforations in the 

 metal with wire-gauze. 



Newman, to meet the objection that strong currents of air, or of gas, could be 

 forced through the gauze, made h lamp with a double wire-gauze, commencing from 

 nearly the top of the flame of the lamp, leaving the lower portion with one gauze 

 only; there was no obstruction to the light, and it has not been found possible to 





