It is chiefly upon the power of collecting the products afforded by coal, with convenience and cheapness, that the promoters of the gas-light illumination found their claims to public encouragement. They conceive that the flame which pit-coal yields, as it is now consumed, is turned to very little advantage: it is not only confined to one place, where a red heat is more wanted than a brilliant flame, but it is obscured, and sometimes entirely smothered, by the quantity of incombustible materials that ascend along with it and pollute the atmosphere. That much inflammable matter is thus lost, is evident from facts that come under our daily observation. We often see a flame suddenly burst from the densest smoke, and as suddenly disappear; and if a light be applied to the little jets that issue from the bituminous parts of the coal, they will catch fire, and burn with a bright flame. A considerable quantity of a gazeous fluid, capable of affording light and heat continually escapes up the chimney, whilst another part is occasionally ignited, and exhibits the phenomena of the flame and light of the fire. The theory of the production of gas-light is therefore analogous to the action of a lamp or candle. The wick of a candle being surrounded by the flame, is in the same situation of the pit-coal exposed to distillation. The office of the wick is chiefly to convey tallow, by capillary attraction, to the place of combustion. As it is decomposed into carburetted hidrogen gas it is consumed and flies off, another portion succeeds; and in this way a continued current of tallow and maintenance of flame are effected. See page 15.