Although the inventor of this lamp expressed himself fully satisfied of its security, yet others have entertained strong doubts on the subject. During the session of parliament for 1835 a committee was appointed to inquire into the Accidents in Mines. The evidence of Mr. Huddle was strongly in favour of the safety of the lamp ; he stated, that for many years he had had not less than 1000,and sometimes 1500 lamps in daily use, and that he never knew in one solitary instance an explosion to happen from them; and he mentioned also that he had been with them in all possible varieties of explosive mixtures. On the other hand abundant evidence, and especially that of Dr. Pereira, was adduced before the committee to show, that In strong currents of explosive mixtures the lamps could not be trusted, as the flame passed through them ; indeed Sir H. Davy seems himself to have been aware that an objection might possibly be urged against them on this head, and he proposed the use of a tin shield where such currents occur. Dr. Turner remarks :—" If a lamp with its gauze red-hot be exposed to a current of explosive mixture, the flame may possibly pass so rapidly as not to be cooled below the point of ignition ; and in that case an accident might occur with a lamp which would be quite safe in a calm atmosphere. It has bten shown by Messrs. Upton and Roberts, that flame may in this case be made to pass through the safety-lamp as commonly constructed ; and I am satisfied, from having witnessed some of their experiments, that the observation is correct. This then may account for accidents in coal-mines where the safety-lamp is constantly employed. An obvious mode of avoiding such an evil is to diminish the apertures of the gauze ; but this remedy is nearly imprac ticable from the obstacles which very fine wire gauze causes to the diffusion of light. A better method is to surround the common safety lamp with a glass cylinder, allowing air to enter solely at the bottom of the Lamp through wire gauze of extreme fineness, placed horizontally, and to escape at top by a similar contrivance." In mentioning the names of other inventors of safety-lamps, we must especially allude to the late George Stephenson ; because some inju dicious friends of Davy have sought to brighten the fame of that great chemist by disparaging the self-taught engineer. In 1815 Stephenson was engine-wright at the Killingworth Colliery, near Newcastle. Terrible explosions having taken place, he turned his ingenious mind to the devising of some kind of lamp which would not prove dangerous. Dr. Clanny of Sunderland had taken up the subject two years before, but had not yet surmounted the difficulties. In the month of August, Stephenson drew out a sketch for a lamp, which, after conferring with Mr. Nicholas Wood and other colliery engineers, was sent to a lamp maker at Newcastle. The new lamp was ready on Oct. 21st, and was tried successfully on the same day. Stephenson then made a few improvements, and caused a new lamp to be ready by Nov. 4th. Again ho experimented and made improvements, and a still more complete lamp was ready by Nov. 30th ; and the " Ocordy" lamp, as the miners familiarly called it, at once came into use at Killingworth. During these very months Davy was at work on the experiments which led to his safety-lamp ; and it is now clearly proved, by the evidence collected in Smiles's ' Life of George Stephenson,' that the illustrious chemist and the humble engine-wright arrived by wholly independent paths at a knowledge of the facts concerning the passage (or rather the non passage) of flame through tubes and small apertures. The coal-miners of the north did justice to Stephenson in a very public way in 1817.
The merits and defects of safety-lamps have formed a subject for many committees of inquiry. The parliamentary committee of 1835 has already been adverted to. A great explosion near Sunderland in 1839 led to the formation of a South Shields committee, the members of which devoted three years to the collecting of evidence relating to the causes of colliery explosions ; and one of the results to which they arrived was, that the safety-lamp might in some circumstances be a source of danger rather than security, if it induced a neglect of measures for ventilating the mines. There was a committee of the
House of Lords appointed in 1849 to inquire into the causes of these terrible disasters ; this was followed by similar committees of the House of Commons in 1852 and the next two years ; and the result of all the inquiries was to show that any one among a large variety of safety-lamps would render useful service, provided care be taken in the using. It is, however, painfully evident that this amount of carp is not always taken; for the miners arc too often thoughtless in the use of their lamps.
In briefly noticing some among the many kinds of safety-lamp devised since the time of Davy, it may be useful to mention that they depend for their safety on two principles—the obstructive action of wire-gauze, and the protective shield afforded by a glass cylinder. Of the Davy lamp enough has been said in former paragraphs; the method of arrangement has only been slightly altered since his day.
The Stephenson lamp has a glass cylinder inside the wire-gauze cylinder. The air is supplied through a triple circle of small holes in the metal bottom. Inside the top of the glass cylinder is a sort of metal chimney. full of small holes. The lamp gives a steady light by being protected from the currents of the mine. It has a few advan Lagar over the fiery, but is generally considered by miners not quite renal is eectuity to some others preeently to be noticed. If the glass ryhader breaks, the lamp becomes a common wire-gauze lump, but with rather too large a diameter; fur it is found that if the diameter le more than about 1 j inches, too groat a volume of explosive gas might by contained within it.
The Smith lamp, a modification of the Stephenson, admits the air through the wire gaunt as well as through theperforations in the metal plate; and there are other arrangements for preventing the of the perforations by dust and oil—an evil to which the lamp is subject.
Clenay lamp has an apparatus for extinguishing the flame in an explosive mixture, when the flame is of sufficient strength to extend itself high in the lamp. The flame melt. a thin wire, which lets tall a shield or extinguisher, so placed as to put out the gas-flame, leaving a very small ea-fleme sufficient to light the minor away from the dangerous place. Dr. Clanny has devoted a large amount of atten lion to the minor detail. of the lamp, especially to the mode of admitting air for combustion.
The Upton and Roberts lamp has a glass cylinder outside the wire-, Rause cylinder. The air is admitted through horizontal apertures just over the °Wearer), and then ham to fellow an intricate route before it can mach the wick. A. a warning of the presence of foul air in the mine, it is the most sensitive of all the safety-Lampe; but this sensi tiveoess is the very cause of the lamp not being much used, for its light is either dimmed or actually put out by causes very likely to occur in a ocal-pit ; and the miners hence dislike it, although it is spoken very highly of by scientific men, who test it in their laboratories.
The Martin lamp has no wire-gauze. The air Is admitted through perforations in a metal bottom to the wick. The body of the lamp is a glass chimney, on the top of which in a copper chimney contracting gradually to a cone. It is very delicate in its action, extinguishing itself almost on the approach of earburetted hydrogen. This would, hoverer, render it useless in a very fiery mine ; besides which, an unprotected glans cylinder, without wire-gauze inside or oat, is considered dangerous.