60 THE POPULAR SCIENCE MONTHLY. 



in course of construction in the north of Ireland (which when com- 

 pleted will have a length of twelve miles) a separate conductor will be 

 provided by the side of the railway, and the return circuit completed 

 through the rails themselves, which in that case need not be insulated ; 

 secondary batteries will be used to store the surplus energy created in 

 running down-hill, to be restored in ascending steep inclines, and for 

 passing roadways where the separate insulated conductor is not practi- 

 cable. The electric railway possesses great advantages over horse 

 or steam power for towns, in tunnels, and in all cases where natural 

 sources of energy, such as water-falls, are available ; but it would not 

 be reasonable to suppose that it will in its present condition compete 

 with steam propulsion upon ordinary railways. The transmission of 

 power by means of electric conductors possesses the further advantage 

 over other means of transmission that, provided the resistance of the 

 rails be not very great, the power communicated to the locomotive 

 reaches its maximum when the motion is at its minimum that is, in 

 commencing to work, or when encountering an exceptional resistance 

 whereas the utmost economy is produced in the normal condition of 

 working when the velocity of the power-absorbing nearly equals that of 

 the current-producing machine. 



The deposition of metals from their solutions is perhaps the oldest 

 of all useful applications of the electric current, but it is only in very 

 recent times that the dynamo-current has been practically applied to 

 the refining of copper and other metals, as now practiced at Birming- 

 ham and elsewhere, and upon an exceptionally large scale at Ocker, in 

 Germany. The dynamo-machine there employed was exhibited at 

 the Paris Electrical Exhibition by Dr. "Werner Siemens, its peculiar 

 feature being that the conductors upon the rotating armature con- 

 sisted of solid bars of copper thirty mm. square, in section, which were 

 found only just sufficient to transmit the large quantity of electricity 

 of low tension necessary for this operation. One such machine con- 

 suming four-horse power deposits about three hundred kilogrammes of 

 copper per twenty-four hours ; the motive-power at Ocker is derived 

 from a water-fall. 



Electric energy may also be employed for heating purposes, but in 

 this case it would obviously be impossible for it to compete in point of 

 economy with the direct combustion of fuel for the attainment of ordi- 

 nary degrees of heat. Bunsen and Sainte-Claire Deviile have taught us, 

 however, that combustion becomes extremely sluggish when a tem- 

 perature of 1,800 C. has been reached, and for effects at temperatures 

 exceeding that limit the electric furnace will probably find advanta- 

 geous applications. Its specific advantage consists in being appar- 

 ently unlimited in the degree of heat attainable, thus opening out a 

 new field of investigation to the chemist and metallurgist. Tungsten 

 has been melted in such a furnace, and eight pounds of platinum have 

 been reduced from the cold to the liquid condition in twenty minutes. 



