I thought the best way to explain the little delusion under which the worthy gardener labored was to refer him to what takes place in his own domain. I asked him wherein lies the advantage of putting his tender plants into his greenhouse in November. How does that preserve them through the winter? How is it that even without artificial heat the mere shelter of the glass will often protect plants from frost? I explained to him that the glass acts as a veritable trap for the sunbeams; it lets them pass in, but it will not let them escape. The temperature within the greenhouse is consequently raised, and thus the necessary warmth is maintained. The dwellers on this earth live in what is equivalent, in this respect, to a greenhouse. There is a copious atmosphere above our heads, and that atmosphere extends to us the same protection which the glass does to the plants in the greenhouse. The air lets the sunbeams through to the earth's surface, and then keeps their heat down here to make us comfortable. When you climb to the top of a high mountain you pass through a large part of the air. This is the reason why you feel warmer on the surface of the earth than you do on the top of a high mountain. If, however, it were possible to go very much closer to the sun; if, for example, the earth were to approach within half its present distance, it is certain that the heat would be so intense that all life would be immediately scorched away. It will be remembered that when Nebuchadnezzar condemned the unhappy Shadrach, Meshach, and Abednego to be cast into the burning fiery furnace, he commanded in his fury that the furnace should be heated seven times hotter than it was wont to be heated. Let us think of the hottest furnace which the minions of Nebuchadnezzar could ever have kindled with all the resources of Babylon; let us think indeed of one of the most perfect of modern furnaces, in which even a substance so refractory as steel, having first attained a dazzling brilliance, can be melted so as to run like water; let us imagine the heat-dispensing power of that glittering liquid to be multiplied sevenfold; let us go beyond Nebuchadnezzar's frenzied command, and imagine the efficiency of our furnace to be ten or twelve times as great as that which he commanded--we shall then obtain a notion of a heat-giving power corresponding to that which would be found in the wonderful celestial furnace, the great sun in heaven. [Illustration: SIR ROBERT BALL. From a photograph by Russel & Sons, London.]