was estimated by Professor Ansted in 1851 at thirty-five million tons; and the value at nine millions sterling at the pit-mouth, and eighteen millions at the place of consumption. The capital engaged in the coal trade was then valued at ten millions. In 1847 the annual value of all the precious metals raised throughout the world was estimated at thirteen millions sterling. That value has been increased within a few years. But the coal of Great Britain, as estimated by the cost at the pit's mouth, is above two-thirds of this value of the precious metals seven years ago; and the mean annual value, at the furnace, of iron smelted by British coal being eight millions sterling, the value together of our iron and our coal exceeds the value of all the gold and silver of South America, and California, and Australia, however large that amount has now become. How the value of our cast iron has been increased by modern science may be in some degree estimated by a consideration of what the hot-blast has accomplished. The hot-blast blows hot air into the iron-furnace instead of cold air. The notion seems simple, but the results are wonderful. The inventor, Mr. Neilson, has seen since 1827 the production of iron raised from less than seven hundred thousand tons to two million two hundred thousand tons. The iron is greatly cheaper than a quarter of a century ago, for only about one-half the coal formerly used is necessary for its production. That production is almost unlimited in amount. In 1788 we produced only sixty thousand tons, or one-thirty-sixth part of what we now produce. The beautiful iron bridge of Colebrook-dale, erected in 1779, consumed three hundred and seventy-eight tons of cast iron. The wonderful Britannia Bridge which has been carried over the Menai Strait, hung in mid air at the height of a hundred feet above the stream, has required ten thousand tons of iron for its completion. If chemistry and machinery had not been at work to produce more iron and cheaper iron, how would our great modern improvements have stopped short--our railroads, our water-pipes, our gas-pipes, our steam-ships! How should we have lacked the great material of every useful implement, from the gigantic anchor that holds the man-of-war firm in her moorings, and the mighty gun that, in the last resort, asserts a spirit without which all material improvement cannot avert a nation's decay,--to the steel pen with which thoughts are exchanged between friends at the opposite ends of the earth, and the needle by which the poor seamstress in her garret maintains her place amongst competing numbers. [Illustration: The first iron bridge, Colebrook Dale.]