382 ON COMBUSTION IN RAREFIED AIR. 
lst Series. 
Pressure of air in inches of Illuminating power of experimental 
flame, 
29:9 100: 
24°9 75'0 
19:9 52°9 
14-6 20-2 
9.6 5.4 
6.6 oo 
2nd Series. 
30°2 100° 
28:2 91°4 
26°2 80°6 
24:2 73:0 
22°2 61°4 
20:2 47°8 
18°2 37°4 
16:2 29:4 
142 19°8 
12:2 125 
10:2 3'6 
“These numbers indicate that even the natural oscillations of 
atmospheric pressure must produce a considerable variation in the 
amount of light emitted by gas-flames, and it was therefore important 
to determine, by a special series of observations, this variation in 
luminosity within, or nearly within, the usual fluctuations of the 
barometrical column. In order to attain greater delicacy in the 
pressure readings in these experiments, a water-guage was used, 
but its indications are translated into inches of mercury in the 
following tabulated results, each of which represents, as before, the 
average of twenty observations. 
3rd Series. 
Pressure of air in inches of mercury. Illum. power of exp. flame. 
30°2 100: 
29:2 95:0 
28:2 89°7 
27:2 8404 
