Fuel is no small item in the annual expenditure of the stove, green-house, and conservatory departments, and therefore deserves consideration.

The specific heat of water being 1, and that of atmospheric air 0.00035, or 1/2850th, if the quantity of fuel which will heat a cubic foot of water one degree be multiplied by 0.00035, the pro-16 duct will be the quantity of fuel required to heat a cubic foot of air, one degree; and twenty times that quantity will heat it twenty degrees; thirty times will heal it thirty degrees, and so on. Now 0.0075 lbs. of best coals will heat a cubic foot of water one degree; therefore 0.000002625 lbs. of best coals will heat a cubic foot of air one degree.

It is essential to good and profitable fuel that it should be free from moisture; for unless it be dry, much of the heat which it generates is consumed in converting that moisture into vapour: hence the superior value of old dense, dry wood, to that which is porous and damp. A pound of dry will heat thirty-five pounds of water from 32° to 212°; but a pound of the same wood in a moist or fresh state, will not similarly heat more than twenty-five pounds. The value, therefore, of different woods for fuel is nearly inversely as their moisture: and this may be readily ascertained by finding how much a pound weight of the shavings of each loses by drying during two hours, at a temperature of 212°.

The preceding are the average of results obtainable in a common well-constructed furnace. By a complicated form of boiler, perhaps a small saving of fuel, in obtaining the same results, may be effected; but it will be found generally, that the original cost of apparatus, and the current additional expense for repairs, will more than exceed the economy of fuel. - Prin. of Gard.