In warming a room, if an open fireplace be used, a good deal depends upon the mode of managing the fire. Servants are very apt to throw on a quantity of coals at once, in such a manner as to smother up the flame; and, when this is the case, the heated air produced by the imperfect combustion of the coals passes up the chimney with the smoke, and very little warmth enters the room. If, on the contrary, the coals are carefully arranged on the fire so as to allow a free current of air to pass through them, perfect combustion takes place, and the coals become a glowing mass, from which rays of light and heat spread in every direction; while the cheerful appearance of a bright glowing fire must be felt by every one. Where an opportunity occurs of altering a fireplace, its capability for diffusing radiant heat will be greatly increased by making the back and sides of fire-brick or fire-stone; as these substances retain heat much longer than any kind of metal, and are consequently more likely to prevent the fire from being chilled by the addition of fresh coal. Drying the coal before burning it is an excellent plan to prevent smoking, as it makes the fire exceedingly bright and fierce. It is true that the coal appears to vanish with extraordinary rapidity, but the combustion is so complete, that a much greater quantity of radiant heat is evolved from the same quantity of fuel. In many country places it is convenient to burn wood, especially where the fireplaces are large, as wood burns best on the hearth, or with the logs supported by what are called andirons or dogs; and fires of this kind harmonise admirably with large rooms and the general appearance of the fittings up of an old country-house. A wood fire, however, requires a good deal of attention to manage it well, as, without care, it will often go out before the logs are half burnt; especially when wood is burnt in a grate, unless it is mixed with a little coal, and there is a plate at the bottom of the grate to keep in the ashes. It must also be remembered, that, though large logs are very useful to make a large fire, yet, when a quick supply of heat is required, it is best to use wood cut into short thick pieces; and that wood burns much better when dry than when green. Green wood, indeed, contains about one-third of its weight of water, which of course evaporates in the shape of vapour, and this vapour aids in carrying the heat up the chimney; dry wood, on the contrary, produces a clear bright fire, which gives out radiant heat. Opinions differ as to what kind of wood is best for fuel. Pine wood burns freely, from the quantity of turpentine it contains, but it does not give out much heat. Beech is preferred on the continent of Europe, and maple in America; but Count Rumford says that the greatest mass of radiant heat is produced by the fuel of the lime tree. Generally speaking, close-grained smooth woods make better fuel than those the grain of which is open and rough.