A HALF-CENTURY OF SCIENCE. 215 



purely chemical methods the constitution of compounds, have not 

 labored in vain. But the future doubtless belongs to physical chem- 

 istry. 



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 (18G9), in which the properties of the ele- 

 ments 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 New- 

 lands about four years before the publication of Mendelejeffs 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 intro- 

 duced 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 proc- 

 ess 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 ship- 

 building 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 



