356 Mr. W. A. Price on the Electrical Resistance of 



it may be mentioned as a curiosity that a particular 4-volt 

 lamp tested at the same time showed a very nearly constant 

 resistance over the same range, the increase of the platinum 

 and the decrease of the carbon resistance just balancing one 

 another. Tiie combination of a carbon lamp and a metallic 

 conductor might be useful for some purposes as having a 

 small or negligible temperature-coefficient. 



7. To determine the effect of external temperature a 50-volt 

 8 c.p. lamp was tested in a paraffin-bath, with the following 

 results : — 



Current in 

 milliamperes. 



Eesi stance in ohms. 



Bath at 7° C. 



Bath at 50° C. 



10 



30 

 50 



70 

 89-98 



160 



150-35 



142-84 



137-14 



131-96 



159 



14997 



142-6 



13683 



13182 



As would be expected, the effect of the external tempe- 

 rature diminishes as the current employed increases. A 

 current of 110-120 milliamperes just made the above lamp 

 incandescent, the above measurements being taken with the 

 filament black. Observations on the lamp in air, quite un- 

 protected, gave closely similar and consistent results, showing 

 that air-draughts outside an exhausted bulb are of no appre- 

 ciable importance. 



8. To ascertain how far the resistance of the lamp is 

 affected by use, the following results were obtained, on a 

 lamp when new, and after it had been run for 6 hours and 

 17 hours respectively at its full voltage of 50 volts. 



Current in 

 milliamperes. 



Resistance in ohms. 



New in air at 11° C. 



6 hrs. run, air 15° C.17hrs. run, air 15° C. 



10 



30 

 50 

 70 

 90 



163 



153-6 



146-2 



140-2 



135-2 



164-7 

 155-5 

 147-7 

 141-4 



164-25 

 155 

 146-45 

 140-5 



135-26 



