THE TANTALUM LAMP. 133 



struct a practical and useful lamp for standard voltages and illu- 

 minating- values, we had to solve the problem of drawing- (he tanta- 

 lum wire in sufficient length down to a diameter of 0"05 millimeter 

 to O'OO millimeter; this we succeeded in doing after long and laI)ori- 

 ous trials. 



In July, 11)03, we possessed the first tantalum lamp with a tilamcnt 

 of about -Of) millimeter diameter. It had a loop-shaped filament 54 

 millimeters long, and it took O'oS amperes at 9 volts and gave 8*5 

 Hefner candlepower at 1 -5 Avatts per candlepower. On the basis 

 of these figures a lamp having the same quality and diameter of wire 

 and working at the same efficiency on a 110-volt circuit would have 

 a filament OoO millimeters long and would give 43 Hefner candle- 

 })ower. The experiinents thus far had proved that the task of pro- 

 ducing lamps for 110 volts and a maximum of 25 to 32 Hefner candle- 

 power was not an easy one in several respects. AVe had to solve the 

 problem of suitably and reliably fixing a filament rather more than 

 2 feet long within a glass globe which should not exceed to any great 

 extent the dimensions of the usual incandescent lamps. The first 

 and most obvious attempt Avns made, of course, by adhering to the 

 loop shape and accommodating the required length of Avire by connect- 

 ing several such bows in series within the lamp. However, lamps 

 made according to this plan with two to four tantalum loo})s gave 

 results which Avere anything l)ut satisfactory. 



It appeared that, like all other metallic filaments Avliich have hith- 

 erto been used for incandescent lamps, tantalum Avire softens sensibly 

 at the temperature attained Avhen Avorked at 1 '5 Avatts per candle- 

 poAver. To use loop-shaped or spiral filaments similar to the carbon 

 filaments of the common incandescent lamps Avas, therefore, out of 

 the question. There Avas no difficulty in suspending the loops, but in 

 that case the lamps Avould have to be used exclusiA^ely in a vertical 

 position, a limitation Avhich Ave Avished to avoid in all circumstances. 

 Besides, such a construction Avould necessitate staying the loops firudy 

 to preA'ent them from becoming entangled with each other during 

 transport of the lami)s. Xor did lamps made with looi)s of corrugated 

 Avire (fig. 1) or of plain or corrugated metal ribbon give satisfaction; 

 for although the looj^s Avere certainly shorten.ed in this Avay, there 

 Avere other draAvbacks Avhich caused us to abandon this construction. 

 It soon became apparent that the one road to success lay in the direc- 

 tion of diA'iding the filament into a number of short straight lengths 

 supported at their ends by insulated holders. In this manner Ave suc- 

 ceeded at last, in September, 11X)3. in producing the first really serv- 

 iceable lamps for about 110 volts. This lamp is illustrated in figure 2. 

 and it Avill be seen that it contains Iavo glass disks cast to a central 

 Avire holder; each disk carries laterally tAA'eh'e arms having small 

 hooks at their ends and insuhite(l from each other. Through these 



