642 
DE. E. EEAKKLAOT) ON THE INELHENCE OE ATMOSPHEEIC PEESSTJEE 
Second Series. 
Pressure of air 
in receiver in 
ins. of mercury. 
Mean illumi- 
nating power. 
Experimental. 
Mean illumi- 
nating power. 
Eeduced. 
30-3 
118-8 
100-0 
28'2 
108-6 
91-4 
26-2 
95-7 
80-6 
24-2 
86-8 
73-0 
22-2 
73-9 
61-4 
20-2 
56-8 
47-8 
18-2 
44-4 
37-4 
16-2 
34-9 
29-4 
14-2 
23-6 
19-8 
12-2 
14-9 
12-5 
10-2 
4-3 
3-6 
These numbers show that even the natural oscillations of atmospheric pressure produce 
a considerable variation in the amount of light emitted by gas-flames; and as such a 
variation is of interest from a technical point of view, it appeared to me of sufficient 
importance to warrant a special series of observations 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-gauge was substituted for a mercurial 
one, but its indications are translated into inches of mercury in the following tabulated 
results : — 
Third Series. 
No. of 
Obser- 
vation. 
Illuminating power of Experimental Elame compared with 
Standard Elame at 100. 
Pressure of air in receiver = 
27’2 in. of mercury. 
28'2 in. of mercury. 
29'2 in. of mercury. 
30'2 in. of mercury. 
1 
70-1 
75-5 
77-8 
83'7 
2 
70-1 
74-5 
77-8 
84-1 
3 
70-4 
73-8 
78-8 
84-1 
4 
701 
73-8 
79-9 
83-7 
6 
70-1 
73-8 
77-8 
83-7 
6 
70-4 
74-2 
77-8 
83-7 
7 
701 
73-8 
77-8 
83-4 
8 
70-1 
74-2 
77-8 
83-4 
9 
70-4 
74-5 
80-2 
83-4 
10 
70-1 
74-5 
80-2 
83-4 
11 
701 
74-8 
79-8 
830 
12 
70-4 
74-8 
79-2 
83 0 
13 
701 
74-5 
80-5 
82-7 
14 
70-4 
74-8 
78-8 
83-0 
15 
70-4 
75-5 
79-8 
82-7 
16 
70-2 
75-5 
79-8 
83-0 
17 
70-1 
75-5 
78-8 
830 
18 
70-7 
75-5 
80-2 
83-4 
19 
70-7 
75-5 
79-8 
83-4 
20 
70-7 
75-1 
80-5 
83-7 
Mean 
70-3 
74-7 
79-2 
83-4 
