The combustion of oil by means of a lamp depends on similar circumstances. The tubes formed by the wick serve the same office as a retort placed in a heated furnace through which the inflammable liquid is transmitted. The oil is drawn up into these ignited tubes, and is decomposed into carburetted hidrogen gas, and from the combustion of this gas the illumination proceeds. See p. 15. What then does the gas-light system attempt? Nothing more than to generate, by means of sufficient furnaces and a reservoir of sufficient capacity, desired quantities of the gas, which is the same material of the flame of candles or lamps; and then by passing it through pipes to any desired distance, to exhibit it there at the mouths of the conducting tubes, so that it may be ignited for any desired purpose. The only difference between this process and that of an ordinary candle or lamp, consists in having the furnace at the manufactory, instead of its being in the wick of the candle or lamp--in having the inflammable material distilled at the station, instead of its present exhibitions in oil, wax, or tallow, and then in transmitting the gas to any required distance, and igniting it at the orifice of the conducting pipe instead of igniting it at the apex of the wick. The principle is rational, and justified by the universal mode in which all light is produced. Indeed, this discovery ranks among the numerous recent applications of chemical science to the purposes of life, which promise to be of the most general utility. It is evident from the outline here given of the production and application of coal-gas, that all the uses of pit-coal are not exhausted; it will be sufficient to observe, that the complete analysis of coal, which has been hitherto confined to the laboratory of the chemist, requiring skill and nicety in the operator, and attended with great trouble and expence, is now so far simplified, that many chaldrons of coals may be decomposed by one gas-light apparatus in the space of six hours, and all the component parts produced in their most useful shape, at an expence out of all proportion below the value of the products. SKETCH OF THE RISE AND PROGRESS OF THE DISCOVERY AND APPLICATION OF COAL-GAS, AS A SUBSTITUTE FOR PROCURING ARTIFICIAL LIGHT. To assist the reader in comprehending the nature and object of substituting coal-gas for tallow or oil, for the purpose of obtaining light, it may be proper to touch slightly upon the successive discoveries that have been made as to the decomposition of coal, and the application of its different ingredients. Such a sketch will add to the many examples that occur in the history of science and art, showing the slow progress of mankind in following up known principles, or extracting from acknowledged facts every possible advantage.