But the most valuable contribution to the Machine in 1855 was Henry Bessemer's epochal invention of making steel by blowing air through molten cast iron, until enough of the carbon had been burnt off to leave a steel of whatever quality was desired. This invention reduced the cost of making steel, and the time required, in so great a degree as to place the manufacture of steel on a basis entirely new, and to extend its field of employment greatly. And, as with many previous great inventions, this one paved the way for still other inventions, by indicating the possibility of still wider fields. The Bessemer process is not in the class with the typewriter or the telegraph, but in the class with the gun; for it does things itself. It would be difficult to specify any invention (except one produced at a much earlier time) that has had more influence, and more good influence, on history than Bessemer's. No one can look out of his window in any town or city, without seeing some of the innumerable products of Bessemer's idea. * * * * * Our record has now brought us to the middle of the nineteenth century. The conditions of living in 1850 were greatly different from those of 1800. In fifty years, the physical conditions of living and of carrying on business of all kinds, had improved more than in the century between 1700 and 1800, more than in the two centuries preceding 1700, and more than in the ten centuries from 500 and 1500. Rapid transportation over the land in railroad trains for both passengers and freight had largely replaced the slow transportation methods of 1800; and, in an almost equal degree, steam transportation at sea had replaced transportation by sails. The printing press had been developed from a crude and slow contrivance, worked by a hand, to a magnificent mechanism worked by steam: the electric battery had been improved into an appliance of the utmost reliability and usefulness; telegraph lines stretched over the continents, and messages were sent surely and instantaneously over hundreds of miles of land; and the science of chemistry had arisen from the ashes of alchemy. As a result of this, the science of photography had been born, and had already begun its work, so varied and so useful. Physics had grown so surely and so greatly, that it had been divided into the separate but allied sciences of heat, light and electricity--including magnetism: the science of engineering had expanded so widely, that it also had been divided into other sciences--civil engineering, mechanical engineering, hydraulic engineering and electrical engineering: the science of medicine, because of the advances in chemistry and physics, had advanced at an equal rate: the gun had been so greatly improved, and gunpowder also, that such a degree of precision and range had been attained as to make the gun of 1800 seem crude indeed; and the improvement had been inevitably caused by the greater knowledge placed at the