'Is it possible,' says Professor Newcomb, 'to convey to the mind any adequate conception of the scale on which natural operations are here carried on? If we call the chromosphere an ocean of fire, we must remember that it is an ocean hotter than the fiercest furnace, and as deep as the Atlantic is broad. If we call its movements hurricanes, we must remember that our hurricanes blow only about 100 miles an hour, while those of the chromosphere blow as far in a single second. They are such hurricanes as, coming down upon us from the north, would, in thirty seconds after they had crossed the St. Lawrence, be in the Gulf of Mexico, carrying with them the whole surface of the continent in a mass not simply of ruin, but of glowing vapour.... When we speak of eruptions, we call to mind Vesuvius burying the surrounding cities in lava; but the solar eruptions, thrown 50,000 miles high, would engulf the whole earth, and dissolve every organized being on its surface in a moment. When the mediæval poets sang, "Dies iræ, dies illa, solvet sæclum in favilla," they gave rein to their wildest imagination without reaching any conception of the magnitude or fierceness of the flames around the sun.' The subject of the maintenance of the sun's light and heat is one that scarcely falls within our scope, and only a few words can be devoted to it. It is practically impossible for us to attain to any adequate conception of the enormous amount of both which is continually being radiated into space. Our own earth intercepts less than the two thousand millionth part of the solar energy. It has been estimated that if a column of ice 2-1/4 miles in diameter could be erected to span the huge interval of 92,700,000 miles between the earth and the sun, and if the sun could concentrate the whole of his heat upon it, this gigantic pillar of ice would be dissolved in a single second; in seven more it would be vaporized. The amount of heat developed on each square foot of solar surface is 'equivalent to the continuous evolution of about 10,000 horse-power'; or, as otherwise stated, is equal to that which would be produced by the hourly burning of nine-tenths of a ton of anthracite coal on the same area of 1 square foot. It is evident, therefore, that mere burning cannot be the source of supply. Lord Kelvin has shown that the sun, if composed of solid coal, would burn itself out in about 6,000 years.