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 countless wheels and pieces of machinery; there are iron vessels on every ocean, and objects of every size made of iron, from the smallest nails up to hundred-ton guns. There is also at this moment, and every moment, a good deal of hot iron on the earth. While I write, iron is doubtless flowing from blast furnaces in England, Wales, and Scotland; while I write, ingots of white-hot Bessemer steel are being dealt with under the steam-hammer or in the rolling-mills; while I write, horse-shoes are being forged, and, at each moment, in one way or another, pieces of iron of every temperature could be found, from those which are as cold as the iron apparatus used by Sir James Dewar in his experiments in the liquefaction of air, up to the glittering melted steel which is poured from the tilted converter. But it must be admitted that the highly-heated pieces of iron bear a very small proportion indeed to the total mass of iron in the world at any moment. No doubt there are many tons of iron now white-hot, but there are many millions of tons of iron once white-hot, but now no warmer than the air around. At certain phases in its history every piece of iron has to undergo the operation of being raised to incandescence, or even of being transformed into a liquid. But the laws of cooling are such that, as soon as the opportunity is afforded, the iron parts with its redundant heat and returns to a stable condition, in which it is at the temperature of the air.

Suppose that some percipient being, who was viewing this earth from above, could only recognise iron when it was red-hot or white-hot, but that he had every facility for perceiving such iron as happened to be in this condition. With such faculties, he would, no doubt,