394 Prof. Ayrton and Mr. Medley on 



of the lamps whose behaviour the curves illustrate, and, as 

 seen from the table on fig- 1 the curves marked I. are drawn 

 from results obtained from lamps which initially required 

 from 2 to 2*5 watts per candle ; for curves marked II. the 

 initial consumption was 2*5 to 3 watts per candle ; for curves 

 111. from 3 to 3*5 ; for curves IV. from 3*5 to 4 ; and for 

 curves V. above 4 watts per candle. 



These curves show that the fall in candle-power varied 

 from 40 to 65 per cent, in 1*200 hours, or, rejecting lamps 

 having as low an initial consumption as from 2 to 2'5 watts 

 per candle, Mr, Feld man's curves would lead us to expect 

 that the candle-power of an average lamp would fall about 

 40 per cent, in 1000 hours. 



From the curves marked A in fig. 3, which give the results 



Fio-. 3. — Prof. Thomas' American Tests. 



of Professor Thomas' tests made in 1892 on 127 lamps of 13 

 American makes, it can be seen that the average American 

 lamp of that date dropped about 43 per cent, in candle- 

 power in 1000 hours, the watts per candle in the same time 

 rising from 4*2 to 6*9. The curves marked M on the same 

 figure show the results obtained from the best make of lamp 

 tested by Professor Thomas ; the average of the 10 lamps 

 tested showed a drop of 30 per cent, in candle-power in 1000 

 hours, and a rise from 4'8 to 6*1 in watts per candle. 



In September 1892 M. Haubtmann published tests on 



