BE7IEWS — MATHEMATICAL AND PHYSICAL SCIENCE. 379 



The lamentable loss of life occurring in coal mines from explosions of fire-damp 

 or inflammable air disengaged from the workings, had for many years attracted the 

 attention and sympathy of the public, and had likewise been carefully considered 

 by scientific men. The explosive gas was known to be the light carburetted 

 hydrogen. Two plans alone seemed to present themselves for diminishing the 

 danger •, — the one, to remove, or chemically to decompose the tire-damp altogeth- 

 er ; the other, to provide a miners' lamp which, by its construction, should be 

 incapable of causing explosion. The former of these modes of protection, it was 

 soon seen, could only be palliative ; the only efficient form which it took was that 

 of a more effectual ventilation; but the terrific rapidity with which a mine may 

 be suddenly invaded by fire-damp, from channels opened by a single blow of the 

 pickaxe, must prevent it from ever acting as a cure. The latter plan had as yet 

 yielded nothing more effectual than the steel mill long used by miners, which pro . 

 duced an uncertain and intermitting light, by the rotation of a steel wheel against 

 a flint, the scintillations of which were incapable of inflaming the fire-damp. 

 The insufficiency of the light prevented it from being used, except in circum- 

 stances of known danger. The celebrated Baron Humboldt, Dr. Clauny, and 

 several others had invented safety lamps on different principles, but they were 

 all clumsy and more or less ineffectual. 



At last, in the summer of 1S15, the Rev. Dr. Gray; (afterwards Bishop of 

 Bristol,) then Chairman of a committee appointed by a benevolent association at 

 Bishop "Wearmouth for the prevention of colliery acccidents, applied to Davy, who 

 was then on a sporting tour in Scotland, requesting his advice and assistance. Sir 

 Humphry answered the call with promptitude. On his southward journey, in the 

 latter part of August, he visited the collieries, ascertained the circumstances of 

 the danger which he had to meet, and was provided by Mr. Buddie with speci- 

 mens of the inflammable air for examination. Within a fortnight after his return 

 to Loudon, he had ascertained new and important qualities of the substance, and 

 had already four schemes on hand for the prevention of accident. Before the end 

 of October, he had arrived at the following principles of operation in connection 

 with a safety-lamp : — " First. A certain mixture of azote and carbonic acid pre- 

 vents the explosion of the fire-damp, and this mixture is necessarily formed in 

 the safe-lantern. Secondly. The fire-damp will not explode in tubes or feeders of 

 a certain small diameter. The ingress to, and egress of air from any lantern," he 

 adds, " is through such tubes or feeders ; and, therefore, when an explosion is arti- 

 ficially made in the safe-lantern it does not communicate to the external air." 

 The effect of narrow tubes in intercepting the passage of flame is due to the cooling 

 effect of their metallic sides upon the combustible gases of which flame is com- 

 posed;* and one of his first and most important observations was the fortunate 

 peculiarity that fire-damp, even when mixed with the amount of air most favor- 

 able to combustion (1 part of gas to 7 or 8 of air), requires an unusually high 

 temperature to induce combination. Olefiant gas, carbonic oxide, and sulphur- 

 etted hydrogen are all inflamed by iron at a red heat, or ignited charcoal, but 

 carburetted hydrogen does not take fire under a perfect white heat. The earliest 

 safety -lamp consisted of a lantern with horn or glass sides, in which a current of 

 air to supply the flame was admitted below by numerous tubes of small diameter 



* This prime fact Davy had obtained from a committee of the R. S. which had been ap- 

 pointed to examine the possibility of gas-explosions being caused by the flame running 

 back through the piping into the gasometer. 



