282 E. L. Nichols — Aye-coating in Incandescent Lamps. 



Conditions after 90S hours. 

 Volts. Amperes. Ohms. Caudle-power. "Watts per candle. 



36-14 1-14 31-70 (unknown)* 



Light transmitted by the coating after 90S hours. 



A =-750 86-6 per cent A = -507 84-5 per cent 



•713 85-2 -481 85 -0 



•635 83-1 -460 85-5 



•580 83-6 -443 86*0 



•538 84-5 -429 86*0 



The normal life of a lamp starting at 5 watts per candle, is 

 many thousands of hours. Lamp No. 10 was prematurely 

 broken at 908 hours, at which time the coating had reached a 

 density corresponding to that of a 3 watt lamp (No. 2) after 

 200 hours of life. A comparison of Tables I and II will show 

 that while the coatings on these two lamp bulbs were not 

 quite neutral nor precisely identical in tint, that they both 

 transmit light with much greater uniformity than do such 

 materials, for example as optical glass, calcite, etc.f 



II. 



The distribution of the age-coating within the bulb. 



The distribution of the age-coating was determined indi- 

 rectly, -as follows : Two of the lamps under examination, were 

 measured for horizontal candle-power according to the " Frank- 

 lin Institute " method \\ measurements being made in twelve 

 meridians, 30° apart. The readings were repeated at frequent 

 intervals throughout the life of the lamps. The results were 

 plotted with polar coordinates. They show (figure 1), by the 

 diminishing area of the successive curves, the progressive loss 

 of brightness due to age, of which about one-half is ascribable 

 to the coating. The similarity of the curves, from first to last, 

 indicates that the coating is deposited uniformly within the 

 bulb, or in uniform lateral zones, so that the density of the 

 film, is symmetrical with reference to any given meridian. 

 The case chosen for illustration is lamp No. 7. The results 

 obtained with lamp 8, were in every essential respect the same 

 as those shown in the diagram. 



* The lamp was broken before the photometric measurements had been com- 

 pleted. 



f See Kruess, Kolorimetrie, p. 243; also, Nichols and Snow, Phil. Mag., V, vol. 

 xxxiii, p 379. 



\ See Franklin Institute Tests (International Electrical Exhibition, 1884), Phila- 

 delphia. 1885. 



