408 Prof. Ayrton and Mr. Medley on 



In these lamps, as in the others we tested, the blackening 

 of the bulbs was very slight indeed. Since the above mea- 

 surements were made, the two lamps whose candle-powers 

 were 11*9 and 11*25 have broken after about another hundred 

 hours of life without, as far as could be judged, any dimi- 

 nution in their light or any increase in the blackening of their 

 bulbs. 



Moreover, although the rise of candle-power seen in figs. 

 10 and 10 a was always accompanied with a rise in current, 

 yet, as the rise in candle-power was proportionally much 

 greater than the rise in current for the lamps we tested, as 

 will be seen from fi gs. 10 and 10 a, where one division re- 

 presents 50 per cent, change in the light, but only 4 per cent, 

 change in the current, the consumption of power per candle 

 was actually less after the lamp had run for 50 hours than 

 it was at the beginning, and the power per candle did not 

 rise seriously during the whole life of a lamp. 



Examining the results for the group run at 100 volts, we 

 see that in the first 124 hours the candle-power rose from 

 26*3 to 35, or by 33*1 per cent., the current in the same time 

 rising from 1*261 to 1*335 amperes, or by 5*87 per cent., so 

 that during these first hours the watts per candle dropped 

 from 4-79 to 3*82. 



During the 1820 hours of running, three lamps broke in 

 this group, their lives being 572, 957, and 1167 hours ; the 

 three still unbroken at the end of the tests had been run for 

 1248, 863, and 653 hours respectively. 



Over the first 500 hours the average consumption of energy 

 with the lamps run at 100 volts was at the rate of 4*0 watts 

 per candle, over the second 500 hours 4*36 watts per candle, 

 over the third 500 hours 4*55 watts per candle, and over the 

 whole run the average efficiency was 0*23 candle per watt, 

 corresponding with 4*35 watts per candle. 



The candle-power of the three lamps run at 101 volts rose 

 in the first 150 hours from 26*5 to 30*6, that is by 15*5 per 

 cent., the current rose from 1*27 to 1*33, or by 4*72 per cent., 

 the watts per candle in the same time falling from 4*80 

 to 4*32. The average watts per candle over the whole run of 

 1340 hours of this group were 4*68, corresponding with an 

 efficiency of 0*215 candle per watt. 



In the group at 102 volts which was run for 1820 hours 

 six lamps broke, their lives being 242, 372, 516, 570, 516, 

 and 786 hours respectively in the order of breaking ; the three 

 lamps unbroken at the end of the tests had run for 1148, 898, 

 and 772 hours respectively. 



The initial rise in candle-power in this group at 102 volts 



