the fumes that you have seen produced from the candle, disperses them throughout the whole of the atmosphere, and carries them away to places where they are wanted to perform a great and glorious purpose of good to man, for the sustenance of vegetation; and thus does a most wonderful work, although you say, on examining it, “Why, it is a perfectly indifferent thing.” This nitrogen in its ordinary state is an inactive element; no action short of the most intense electric force, and then in the most infinitely small degree, can cause the nitrogen to combine directly with the other element of the atmosphere, or with other things round about it; it is a perfectly indifferent, and therefore to say, a safe substance. But before I take you to that result, I must tell you about the atmosphere itself. I have written on this diagram the composition of one hundred parts of atmospheric air:— Bulk. Weight. Oxygen, . . . . . 20 22.3 Nitrogen, . . . . 80 77.7 ——— ————— 100 100.0 It is a true analysis of the atmosphere, so far as regards the quantity of oxygen and the quantity of nitrogen present. By our analysis, we find that 5 pints of the atmosphere contain only 1 pint of oxygen, and 4 pints, or 4 parts, of nitrogen by bulk. That is our analysis of the atmosphere. It requires all that quantity of nitrogen to reduce the oxygen down, so as to be able to supply the candle properly with fuel, so as to supply us with an atmosphere which our lungs can healthily and safely breathe; for it is just as important to make the oxygen right for us to breathe, as it is to make the atmosphere right for the burning of the fire and the candle. But now for this atmosphere. First of all, let me tell you the weight of these gases. A pint of nitrogen weighs 10⁴⁄₁₀ grains, or a cubic foot weighs 1⅙ ounce. That is the weight of the nitrogen. The oxygen is heavier: a pint of it weighs 11⁹⁄₁₀ grains, and a cubic foot weighs 1¾ ounce. A pint of air weighs about 10⁷⁄₁₀ grains, and a cubic foot 1⅕ ounce. [Illustration: Fig. 25.]