332 THE ADDRESSES, LECTURES, ETC., OF 



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 ordinary degrees of heat. Bunsen and St. Claire 

 Deville have taught us, however, that combustion becomes ex- 

 tremely sluggish when a temperature of 1800 C. has been reached, 

 and for effects at temperatures exceeding that limit the electric 

 furnace will probably find advantageous applications. Its specific 

 advantage consists in being apparently 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 8 pounds of platinum have been reduced from the 

 cold to the liquid condition in 20 minutes. 



The largest and most extensive application of electric energy at 

 the present time is to lighting, but, considering how much has of late 

 been said and written for and against this new illuminant, I shall 

 here confine myself to a few general remarks. Joule has shown 

 that if an electric current is passed through a conductor the whole 

 of the energy lost by the current is converted into heat ; or, if the 

 resistance be localised, into radiant energy, comprising heat, light, 

 and actinic rays. Neither the low heat rays nor the ultra-violet 

 of highest refrangibility affect the retina, and may be regarded as 

 lost energy, the effective rays being those between the red and 

 violet of the spectrum, which in their combination produce the 

 effect of white light.- 



Eegarding the proportion of luminous to non-luminous rays 

 proceeding from an electric arc or incandescent wire, we have a 

 most valuable investigation by Dr. Tyndall, recorded in his work 

 on " Eadiant Heat." Dr. Tyndall shows that the luminous rays 

 from a platinum wire heated to its highest point of incandescence, 

 which may be taken at 1,700 C., formed -J^th part of the total 

 radiant energy emitted, and T Vth part in the case of an arc light 

 worked by a battery of 50 Grove's elements. In order to apply 

 these valuable data to the case of electric lighting by means of 

 dynamo currents, it is necessary in the first place to determine 

 what is the power of 50 Grove's elements of the size used by 

 Dr. Tyndall, expressed in the practical scale of units as now estab- 

 lished. From a few experiments lately undertaken for myself, it 

 would appear that 50 such cells have an electro-motive force of 



