18 B. Silliman on the relation between the intensity of 
The intensity of gas flames, i. e., illuminating power, increases 
(within the ordinary limits of consumption) as the square of — 
the volume of the gas consume 
As the first experimental demonstration of this theorem — 
was made by Mr. William Farmer, the photometric observer — 
at the Manhattan Gas Co’s. works in New York, 1 propose — 
to speak of it as “‘ Farmer’s theorem.” I am also indebted 
courteous Engineer of the Manhattan Gas Light Company, for . 
the free use of their experimental data and the permission to — 
employ them in illustration of Farmer’s theorem 
amental importance of this new mode of ¢ compu- — 
tation will at once appear, if, assuming it for the sake of 
illustration to be true, we apply it to the case already given 4 
above, which then becomes—— 
“5? - 205? ; 40, 
showing an increase of forty per cent over the old rule of © 
correction. Let us - how far this theorem is sustained by — 
the test of yee! meee 
ent 1st 
of the phbtiitheter bar, were made to give exactly the same 
intensity of illumination, This was accomplished of course 
by placing the Bunsen disc midway between the two burners, 
and ce ae the combustion until the disc was perfectly + 
the consumption being noted equal by two wet gas — 
neutra 
meters under the same pressure. The screen was then moved 
upon the bar to a point just four times as far from one flame — 
as it was from the — i : “ the bar being 100 inches, the — 
screen stood at 80, i. e., :4. The light from the distant a 
burner was then ey until the disc again showed an 
equality of illumination. On re the rate of the gas con-— 
sumed by the two burners respec tively, one gave 3°66 cubic — 
feet and the other 7°32 cubic feet, or exactly double, or in other 
words, the lights were as the squares of the volumes of gas 
1:4 
consumed, thus: 3°66? 
_ By the old rule the intensity would have been estimated — 
ly as the volume of the gas consumed, thus 
3°66 : 7 32 = x; 
3°30 ae 
“ 
ee similar gas flames, one at each end 
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