Nothing in the way of inventions can be compared to those of Cort’s as to the effect they have had in promoting the iron industry, until we reach a period some years after the middle of our century; but we must not neglect to recognize the scarcely inferior importance of Rogers’ improvement. Singularly enough, neither of these men reaped any benefit from his inventions. Cort died in the last year of the eighteenth century, quite a poor man, having been supported only by a niggardly pension of some £160 from the Government, and leaving his family in indigent circumstances. Yet a most eminent authority on iron questions (Sir W. Fairbairn) estimated—some time about the middle of our era—that the two inventions of Cort’s alone, the rolling-mill and the reverberatory puddling furnace, had by that time added to the wealth of Great Britain by an amount equivalent to six hundred million pounds sterling. For many iron-masters had profited by these inventions, amassing very great fortunes, in some instances also acquiring titles of honour. Clearly to Cort and Rogers may be applied the _sic vos non vobis_ saying. We shall now turn to the improvements that have been effected in the blast furnace, and of these none perhaps has been more marked than that made by Neilson, when in 1828 he substituted heated air for the ordinary cold air that had before always supplied the blast. It will be remembered that the heat is due to the combination of only the oxygen of the air with the carbon of the coke, but the greater part of the air—the four-fifths of nitrogen—take no part in the action, beyond abstracting a large proportion of the heat; but when the air is heated to a high temperature before entering the furnace, the cooling effect of the nitrogen is greatly obviated, and consequently a much higher temperature is obtained at the place of combustion, and the requisite intensity of heat is at once produced, which is most effective in completing the fusion and separation from each other of the slags and iron, and also in accomplishing the reduction of the oxide. But Neilson found that the net result of burning some fuel to heat the air before entering the furnace was a great economy of the total fuel required for smelting the ore. He had to encounter many difficulties in carrying his invention into practice; the iron ovens first used for heating the air were rapidly oxidized; and when thick cast iron pipes were substituted, these were liable to leak at the joints on account of the expansions and contractions caused by changes of temperature. Then the new invention had as usual to contend with established prejudices and misconceptions; but it soon came into use in Scotland, where it effected a great saving; inasmuch as it was found possible to use with the hot blast raw coal of a certain kind, plentiful in Scotland, because the heat retained by the ascending gases sufficed to convert the coal at the top of the charge into coke.