602 PEOFESSOE BUNSEN AND DE. H. E. EOSCOE’S PHOTO-CHEMICAL EESEAECHES. 
The intensity of the chemical rays proceeding from a constant source of light, was 
measured before and after their passage through a cylinder with plate-glass ends, filled 
with dry chlorine. After the amount of light Iq has passed through the first plane glass 
plate it has become oIq, after having passed through the chlorine it has diminished to 
ablo, and on passing through the second glass plate it will be reduced to abaj-o- The 
amormt of light I which issues from the cylinder, is therefore equal to l=(xba^^ or 
If we determine the amount of light I which passes through the cylinder for various 
intensities of the incident ray lo, and if we find that for the various inteirsities the 
fractioir t- remains constant, we may conclude that the amount of transmitted light is 
proportional to the amount of inciderrt light. 
The following experiments show the equality of the fraction ^ for amounts of light 
varying from 1 to 1‘9. 
Series of Experiments I. 
Exp. 1. 
Exp. 2. 
Exp. 3. 
Exp. 4. 
Exp. 5. 
Exp. 6. 
Exp. 7. 
Exp. 8. 
lo 
13-52 
13-20 
12-85 
13-51 
7-21 
8-34 
12-39 
12-84 
I 
3-63 
3-63 
3-79 
3-79 
2-11 
2-44 
3-69 
3-69 
Hence the values of are — 
Number of 
Experiment. 
I 
Io‘ 
Variation 
from mean. 
Relative intensity 
of light. 
1 
0-267 
-0-019 
1-875 
2 
0-275 
-0-011 
1-830 
3 
0-295 
+ 0-009 
1-782 
4 
0-281 
-0-005 
1-874 
5 
0-293 
+ 0-007 
1-000 
6 
0-293 
+ 0-007 
1-156 
7 
0-298 
+ 0-012 
1-716 
8 
0-287 
+ 0-001 
1-781 
Mean 
0-286 
The conclusion derived from these experiments, viz. that the absorption of the 
chemical rays varies proportionally with the intensity, may serve as the formdation for 
the general law of the extinction of the optical and chemical rays in transparent media. 
For, as it is thus proved that the amount of light transmitted through a medium of 
fiirite thickrress is proportional to the intensity of the incident rays, it may be assumed 
that the same relation wiU hold good for an infinitely thin medium. According to this 
supposition, the relation between the transmitted light I, and the thicknesss of the 
absorbing medium, is found from the equations 
I=Io.lO-^ 
(T) 
