Tests of Glow -Lamps. 405 



An old lamp was taken and wires soldered to its terminals, 

 and also to the terminals of the socket into w r hich it was 

 screwed, and, by measuring as nearly simultaneously as 

 possible the pressures on the lamp and on the socket terminals 

 under various conditions as to heat and position of lamp, we 

 proved that the resistance of the socket and contacts was 

 never perceptible. 



There seemed, therefore, no reason to doubt the results 

 already obtained; but as the accuracy with which the candle- 

 power could be measured had increased with practice and 

 with the introduction of the swinging frame, we decided after 

 110 hours of testing to start again with* new lamps. 



The results obtained in these preliminary tests are shown 

 in fig. 10a, the curves in fig. 10 being those obtained from 

 the lamps subsequently tested. 



These curves show the variation of light and current wdth 

 time for four groups of lamps between the terminals of which 

 perfectly constant P. Us. of 100, 101, 102, and 104 volts were 

 maintained respectively, the full lines representing candle- 

 power and the dotted lines current. The breaks in the curves 

 connected by vertical lines indicate the times at which a 

 lamp broke and was replaced by a new one, so that each 

 group always consisted of three lamps. 



All these curves show that the light given out by these 

 Edison-Swan lamps was greater after they had been glowing 

 for some time than it was when the lamps were new; also that 

 even just before the filament of one lamp in a group broke, 

 the total light given out by the group of three was greater 

 than when the lamps were new. This is a totally different 

 result from that obtained in earlier tests, as illustrated in 

 figs. 1, 2, 3, and 4, which showed that a considerable deterio- 

 ration in candle-pow r er always took place after lamps had 

 been running for some time. ^Further, while the globes of 

 earlier lamps were always much blackened, even after a run 

 of a few hundred hours, and so became comparatively useless 

 long before the filament broke, the Edison-Swan lamps which 

 we have been testing showed hardly any blackening, even 

 when the filaments lasted for over 1300 hours. 



The highness of the average candle-power of Edison-Swan 

 lamps marked 100-8 after they have been run for some 

 time at 100 volts, is corroborated by the figures in the 

 following table, which gives the results of the measure- 

 ments of the candle-power and the watts per candle of eleven 

 8-candle 100-volt lamps which had been run from the mains 

 of the Notting-Hill Electric Lighting Co. As these lamps 

 had been used in different rooms of a dwelling-house, it was 



Phil. Mag. S. 5. Vol. 39. No. 240. May 1895. 2 E 



