561 
1909-10.] The Efficiency of Metallic Filament Lamps. 
For purposes of comparison I have taken the figures in the second column 
from a paper by H. Hirst.* He gives them as the values generally accepted 
for these lamps, though I think 1*2 watts per candle more accurate for 
tungsten. My value, 2'9, agrees well with Mendenhall’s, 2’8, for carbon ; 
but in order to speak with absolute certainty of the relative merit of the 
different metals, it would be necessary to experiment with a greater number 
of lamps. 
The measurements described in this article were carried out in the 
Physical Laboratory of the University of Glasgow with the assistance of 
a grant from the Carnegie Trust for the Universities of Scotland. 
* “ Kecent Progress in Tungsten Metallic Filament Lamps,” Journ. of El. Eng., xli., 
1908, p. 636. 
( Issued separately December 16, 1910.) 
