Tests of Gloiv-Lamps. 



395 



many European makes of lamps. The curves in fig. 4 show 

 the results he obtained from testing twenty 16 C.P. Edison- 

 Fig. 4. — Tests by M. Haubtmann on 20 similar 16 Candle-Power Edison- 

 Swan Lamps, 10 of which were run at 110 volts and 10 at 

 102 volts. 



Swan lamps, ten at 102 and ten at 110 volts. Those run at 

 102 volts showed a drop of about 30 per cent, in candle-power 

 in 1000 hours, the watts per candle rising in the same time 

 from 3*27 to 4*4 ; the lamps run at 110 volts in 1000 hours 

 dropped 28 per cent, in candle-power and rose from 3*35 to 

 4*58 watts per candle. 



If, now, in the light of the knowledge obtained from these 

 experiments, we look at the equation of cost quoted in the 

 beginning of this paper, we see that some changes must be made 

 in it before it expresses the truth. As originally given it 

 was : — Cost per hour per candle equals 



L{v) x C(v) 



but, as neither the candle-power nor the watts per candle 

 remain constant throughout the life of the lamp, L(v) x G(v) 

 does not give the total candle-hours obtained during the 

 lamp's life, and neither does HxW(u) give the true cost of 

 power per hour per candle. The equation must, therefore, be 

 written : — Cost per hour per candle equals 



, . , ^j — , h H X average watts per candle. 



total candle-hours a l 



