2U 



Mr. M. Evans. Observations on the [Feb. 18, 



intense, and not only caused at times severe burns, but occasionally 

 would even char the little paper labels attached to the glass. 



I also regret not having dissipated by a powerful current the black 

 carbon deposited over the bright surface in the last case, as an increase 

 of economy in working and light-giving should have resulted, and this 

 would have been the more interesting as ordinarily it is just the 

 other way; as soon as by overheating or long use the polished sur- 

 faces of our best lamps are injured, so surely is there an increased 

 waste of energy, and hence the extreme difficulty of preserving 

 lamps made for use as standards for any long period. 



From these results it appears probable that the attainment of 

 economical high E.M.F. lamps of ordinary sizes may be very diffi- 

 cult, as what would be a high E.M.F. lamp with a black surface 

 would be a low E.M.F. lamp were this black surface made bright; 

 the energy required being less, both the E.M.E. and current would 

 have to fall. The desire, therefore, for high E.M.F. lamps should be 

 met not by a supply of black wasteful filaments, but more properly by 

 economical lamps of greatly increased size and candle power, or by 

 lamps of a smaller candle power run two or more in series. 



Diagram 1. 

 Carbon A. Carbon B. 



Table I. Table II. 



Candles. 



Yolts. 



Amp. 



Watts. 



Yolts. 



Amp. 



Watts. 



4 



53 5 



1-12 



60 



385 



1-05 



40-4 



6 



56 



1-2 



67 2 



42 



1-18 



49-5 



8 









43 



1-23 



52 4 



10 



60-5 



1-32 



80 



45 



1-30 



58-5 



12 









46-5 



1-35 



62-5 



14 



63 



1*4 



88-2 



48 



1-41 



67-6 



16 









48-5 



143 



69 3 



18 



65* 



1-46 



94-9 



49 



1-45 



710 



20 



66 5 



1-52 



101 









22 









50-5 



1-52 



76-7 



24 



67 



1-64 



103 









25 















26 









52 



1-58 



82-1 



28 



69 



1-62 



m-7 









30 



69 



1-65 



113 8 



53 



1-65 



87-7 



35 















40 



74 



1-80 



133 -2 



56 



1-78 



99-7 



45 















50 









58-5 



1-9 



101 



55 



77 



1-95 



181 









60 









62 



2-05 



127 



• 



