se ae 
uae ae 
_of hydrogen for 
380 B Silliman on determining the Photometric power of a 
ab + cx _ (d—b)a , 5 
ate - gee Shige 
ab + ce—=ad+ed 
cx = ad+-cd-+- ab. 
And this expression is stated arithmetically in the following 
Rule :—Subtract the intensity of the poor gas from the intensity 
of the mixture; multiply the remainder by the volume of poor gas ; 
divide the product by the volume of rich gas; add to the quotient the 
intensity of the mixed gas, and the sum is the intensity of the rich 
Hence, 
unwarran 
olefines) are diluted by the non-illuminants. It is agreed, on all 
_ temperatures, that they may in fact be called, as to 
uminosity, neutral. It can hardly be questioned that the 
intensity which these neutral gases may assume in a given mix- 
ture must depend, under the same ordinary conditions before 
but it is sufficiently so for photometric purposes. The avidity 
all the olefines, however, renders it difficult to 
