The most beneficial application of gas-lights unquestionably is in all those situations where a great quantity of light is wanted in a small place: and where light is required to be most diffused, the advantages of this mode of illumination are the least.--Hence, as already stated, the lighting of the parish, or street-lamps only, without lighting shops or houses, can never be accomplished with economy. We have noticed before the reason why the price of coals can have little effect upon the gas-light; because the very refuse, or small coals, called slack, which pass through the screen at the pit’s mouth, and which cannot be brought into the market--nay, even the sweepings of the pit, which are thrown away, may be employed for the production of coal-gas. It makes no difference in what form the coal is used, and this circumstance may contribute to enable the coal-merchant to furnish coals in larger masses, and as they come from the mine, instead of increasing the bulk by breaking them into a smaller size,[33] which is a practice commonly adhered to. This unquestionably reduces the value of coals; because the quantity of radiant heat generated in the combustion of a given quantity of any kind of fuel depends much upon the management of the fire, or upon the manner in which the fuel is consumed. When the fire burns bright, much radiant heat will be sent off from it; but when it is smothered up, very little will be generated: most of the heat produced will then be expended in giving elasticity to a thick dense vapour, or smoke, which is seen rising from the fire; and the combustion being very incomplete, the carburetted hidrogen gas of the coal being driven up the chimney without being inflamed, the fuel is wasted to little purpose. [33] It is not generally apprehended, how very wasteful the use of small coals is in the ordinary open fire-grates. Necessity makes us use the poker very much, particularly, when the coals are small; and habit prevails even when they are large. By the constant stirring of the fire almost the whole of the small coal passes through the bars; and consequently a great deal goes to the dust-hole without being burnt at all. To prove this, we need only take a shovel full of ashes and put them into a pail, and then pouring water over them, which being gently run off, will carry away nearly all the light and burnt parts: and leave an astonishing quantity of bright unburnt coal, which has escaped from the fire-place, in consequence of being small.