204 
PROFESSOR TYNDALL ON THE ABSORPTION AND 
When oxygen, hydrogen, or nitrogen was substituted for atmospheric air, no change 
in the position of the galvanometer-needle occurred ; but when any one of the com- 
pound gases was allowed to occupy the space between the plates, a measurable 
deflection ensued. The plates of rock-salt were not so smooth, nor was their parallelism 
so perfect as entirely to exclude the gas when they were in contact. The contact was 
but partial, and hence a stratum of gas sufficient to effect a sensible absorption could 
find its way between the plates even when they touched each other. On this account 
the first thickness in the following Tables was really a little more than 0-01 of an inch. 
The first column in each contains the thickness of the gaseous layer, while the second 
column contains the absorption expressed in hundredths of the total radiation. The 
first layer of carbonic oxide, for example, absorbed 0*2, and the second layer 05 per 
cent, of the entire heat. 
Table I. — Carbonic Oxide. 
Thickness of gas. 
Absorption in 
hundredths of the 
total radiation. 
Thickness of gas. 
Absorption in 
hundredths of the 
total radiation. 
0-01 of 
an inch 
o 
to 
0-4 
of an inch 
... 3-5 
0-02 
99 
... 0-5 
0-5 
op 
cb 
0-03 
99 
... 0-7 
0-6 
99 
... 4-0 
0-04 
... 0-9 
1-0 
99 
... 5-1 
0-06 
99 
7™H 
1-5 
99 
... 6-1 
0-1 
... 1-6 
2-0 
99 
... 6-8 
0-3 
... 3-0 
Table II. — Carbonic Acid. 
Absorption in 
Absorption in 
Thickness of gas. 
hundredths of the 
Thickness of gas. 
hundredths of the 
total radiation. 
total radiation. 
0-01 of 
an inch 
. . . 0-86 
0-4 
of an inch 
. . . 5 - 3 
0-02 
99 
... 1-2 
0-5 
99 
... 5-7 
0-03 
99 
... 1-5 
0-6 
99 
... 5-9 
0-04 
99 
... 1-9 
0-7 
99 
... 6-0 
0-05 
99 
... 2-1 
0-8 
99 
... 6-1 
0-06 
... 2-3 
0-9 
99 
... 6-2 
0-1 
99 
... 3*3 
1-0 
99 
... 6-3 
0*2 
99 
... 4-1 
1-5 
99 
... 7-0 
0-3 
99 
... 4-8 
2-0 
99 
... 7-6 
