E. L. Nichols — Age- coating in Incandescent Lamps. 283 











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III. 



:7%e age-coating considered as a factor in the diminishing effi- 

 ciency of the lamp. 



It may be seen from the Tables (I and II) that the absorbing 

 power of the coating is in itself sufficient to account for a very 

 considerable falling oif in the caudle-power, as the lamp, 

 within the bulb of which it forms, grows old in service. By 

 summation of the values in the tables, we may obtain the 

 average absorbing power for the entire spectrum ; and since 

 selective absorption is almost entirely absent, these averages 

 will give very closely indeed the loss in candle-power, which 

 at the time in question was ascribable to the influence of the 

 coating. From the data in Tables I and II, also, we may com- 

 pute the efficiencies of the lamps at various stages in terms of 

 their initial efficiency as unity ; likewise their brightness from 

 time to time, in terms of their initial candle-power, as unity. 

 In Tables III and TV are given, for purpose of comparison, 

 the relative brightness and efficiency of lamps 2 and 10, at 



