590 Mr. Alexander Siemens [April 23 



WEEKLY EVENING MEETING, 



Friday, April 23, 1909. 



The Eight Hon. Lord Rayleigh, O.M. P.C. M.A. D.C.L. 

 LL.D. F.R.S., in the Chair. 



Alexander Siejiens, Esq., M.Inst. C.E., M.R.I. 

 Tantalum and its Industrial A^jplications . 



When the announcement was made in the year 1878 that "the 

 division of the electric light had been successfully accomplished," 

 many people beUeved that the days of lighting by gas had come to 

 an end, and acted accordingly, much to their own disadvantage : for 

 the competition of the glow-lamp served only to stimulate its rival to 

 new life. 



Burners of improved construction, regenerative burners, and 

 finally gas mantles helped to restore to gas the ground it had lost, 

 and until a short time ago even threatened to check the spreading of 

 electric lighting. 



Not only this growing competition of gas, but the universal 

 necessity of cheapening the production of commodities that are for 

 general use, forced electrical engineers to study in all its aspects the 

 question of improving the efficiency of electric lighting. 



As a guide in their researches they had the well-known principle 

 that the illuminating power of a sohd body increases at a much 

 greater ratio than its temperature, or, in other words, thiit with the 

 increase of temperature a greater percentage of the energy expended 

 for heating the body is converted into light. 



There is plenty of room for improvement ; for even the most 

 economical source of light, the electric arc lamp, converts only about 

 one per cent, of the energy of the electric current flowing through it, 

 into light, the rest appearing as heat, so that in reality all methods 

 of lighting devised by men are, to a much greater extent, methods of 

 heating. 



The first successful incandescent lamp consisted of a carbon 

 filament ; and for a long time carbon appeared to be the only suit- 

 able substance, although the temperature to which such a filament 

 can be raised is limited to about 1600" C, as above this point the 

 carbon begins to disintegrate rapidly. 



At this temperature the lamp consumes from three to three and a 

 half watts per candle-power, while any attempt to produce light more 

 economically by raising the temperature of the filament results only 



