14 
PEOFESSOE TYNDALL ON THE ABSOEPTION AND 
portionality, for small quantities, of density to absorption exhibits itself so decidedly as 
to induce me to give the observations. The first column, as usual, contains the measures 
of vapour, the second the observed absorption, and the third the calculated absorption. 
The galvanometric deflections are omitted, their equivalents being contained in the 
second column. In fact as far as the eighth observation, the absorptions are merely 
the record of the deflections. 
Table IV.- 
Unit- 
—Mixture of Ether Vapour and Air. 
-measure s-oth of a cubic inch. 
Absorption. 
easures. 
r 
Observed. 
Calculated. 
1 
4-5 
4-5 
2 
9-2 
9-0 
3 
13-5 
13-5 
4 
18-0 
18-0 
6 
22-8 
23-5 
6 
27-0 
27-0 
7 
31-8 
31-5 
8 
36-0 
36-0 
9 
39-7 
40-0 
10 
45-0 
45-0 
20 
81-0 
90-0 
21 
82-8 
95-0 
22 
84-0 
99-0 
23 
87-0 
104-0 
24 
88-0 
108-0 
25 
90-0 
113-0 
26 
93-0 
117-0 
27 
94-0 
122-0 
28 
95-0 
126-0 
29 
98-0 
131-0 
30 
100-0 
135-0 
Up to the 10th measure we find that density and absorption augment in precisely the 
same ratio. While the former varies from 1 to 10, the latter varies from 4‘5 to 45. 
At the 20th measure, however, a deviation from proportionality is apparent, and the 
divergence gradually augments from 20 to 30. In fact 20 measures tell upon the rays 
capable of being absorbed ; the quantity destroyed becoming so considerable, that every 
additional measure encounters a smaller number of such rays, and hence produces a 
diminished effect. 
With ether vapour alone the results recorded in the following Table were obtained. 
Wishing to detennine the absorption exercised by vapour of very low tension, the 
capacity of the unit-measure was reduced to x^o^h of a cubic inch. 
