Ten years afterwards came his classical paper “On the Conversion of Dynamical into Electrical Force, without the use of permanent Magnetism,” which was read before the Royal Society on February 14, 1867. Strangely enough, the discovery of the same principle was enunciated at the same meeting by Sir Charles Wheatstone, while there is yet a third claimant in the person of Mr. Cromwell Varley, who had previously applied for a patent in which the idea was embodied. It can never be quite certain, therefore, who was the first discoverer of the principle upon which modern dynamo-machines are constructed. I need not describe here the way in which this principle is carried out in all dynamo-machines. Suffice it to say that they differ from Faraday’s magneto-electric machines in having electro-magnets in the place of permanent steel magnets, and that these electro-magnets are, if I may be allowed the expression, self-excited by the play of mutual give and take between the armature and the magnet. It was the invention of the dynamo-machine which made practicable the application of electricity to industrial purposes. Experiments have shown that it is capable of transforming into electrical work 90 per cent. of the mechanical energy employed as motive power. Its practical application is still in its infancy. In 1785 Watt completed his “improvements” in the steam-engine, and the century which has since elapsed has not sufficed to demonstrate the full extent of its utility. What may we not expect in the next hundred years from the extension of the dynamo-machine to practical purposes? In the development of appliances for the production of the electric light Sir William Siemens took a leading part, and, as is well known, his firm has been _facile princeps_ at all the important electrical exhibitions. But while ever zealous to promote its progress, he never took a partisan view of its utility, candidly admitting that gas must continue to be the poor man’s friend. In 1882 he told the Society of Arts that “Electricity must win the day _as the light of luxury_, but gas will find an ever-increasing application for the more humble purposes of diffusing light.” In the hands of Dr. Siemens the enormous energy displayed in the Electric Arc was applied to other purposes than mere lighting. In June, 1880, he greatly astonished the Society of Telegraph Engineers by exhibiting the power of an electrical furnace designed by him to melt considerable quantities of such exceedingly refractory metals as platinum, iridium, &c. He explained that he was led to undertake experiments with this end in view by the consideration that a good steam-engine converts 15 per cent. of the energy of coal into mechanical effect, while a good dynamo-machine is capable of converting 80 per cent. of the mechanical into electrical energy. If the latter could be expended without loss in an electric furnace, it would doubtless far exceed in economy any known air furnace.