purely chemical methods the constitution of compounds, have not labored in vain. But the future doubtless belongs to physical chemistry.
In connection with the rectification of the atomic weights it may be mentioned that a so-called natural system of the elements has been introduced by Mendelejeff (1869), in which the properties of the elements appear as a periodic function of their atomic weights. By the aid of this system it has been possible to predict the properties and atomic weights of undiscovered elements, and in the case of known elements to determine many atomic weights which had not been fixed by any of the usual methods. Several of these predictions have been verified in a remarkable manner. A periodicity in the atomic weights of elements belonging to the same class had been pointed out by Newlands about four years before the publication of Mendelejeff's memoir.
In mechanical science the progress has not been less remarkable than in other branches. Indeed, to the improvements in mechanics we owe no small part of our advance in practical civilization, and of the increase of our national prosperity during the last fifty years. This immense development of mechanical science has been to a great extent a consequence of the new processes which have-been adopted in the manufacture of iron, for the following data with reference to which I am indebted to Captain Douglas Galton. About 1830, Neilson introduced the hot blast in the smelting of iron. At first a temperature of 600° or 700° Fahr. was obtained, but Cowper subsequently applied Siemens's regenerative furnace for heating the blast, chiefly by means of fumes from the black furnace, which were formerly wasted; and the temperature now practically in use is as much as 1,400°, or even more: the result is a very great economy of fuel and an increase of the output. For instance, in 1830, a blast-furnace with the cold blast would probably produce 130 tons per week, whereas now 600 tons a week are readily obtained.
Bessemer, by his brilliant discovery, which he first brought before the British Association at Cheltenham in 1856, showed that iron and steel could be produced by forcing currents of atmospheric air through fluid pig-metal, thus avoiding for the first time the intermediate process of puddling iron, and converting it by cementation into steel. Similarly, by Siemens's regenerative furnace, the pig-metal and iron ore are converted directly into steel, especially mild steel for shipbuilding and boilers; and Whitworth, by his fluid compression of steel, is enabled to produce steel in the highest condition of density and strength of which the metal is capable. These changes, by which steel can be produced direct from the blast-furnace instead of by the more cumbersome processes formerly in use, have been followed by improvements in manipulation of the metal.
The inventions of Cort and others were known long before 1830, but we were then still without the most powerful tool in the hands of