PEOFESSOK BUNSEN AND DE. H. E. EOSCOE’S PHOTO-CHEMICAL EESEAECHES. 619 
Series of Experiments XV. 
No. of 
Exp. 
w,. 
W. 
h,. 
h. 
1 
y\ 
1. 
8*59 
7-61 
198-3 
55-7 
millims. 
59-3 
2. 
6-61 
4-75 
185-5 
31-0 
56-4 
3. 
8-34 
6-45 
128-0 
48-5 
79-8 
Mean .... 
63-2 
Hence the value of the coefficient of extinction for the standard chlorine mixture at 
0° C. and 0'76 pressure is y, = 0‘01743, and its reciprocal 57'4. 
A negative value is obtained for the coefficient of chemical extinction calculated from 
the results of Experiments XIV. and XV. From this we may conclude, that the rays 
which produced the action in Experiments XIV. possessed a different degree of refrangi- 
bility from those which acted in Experiments XV., and that from this reason the two 
series of experiments are not comparable ; this view is easily explained by the fact, that 
the experiments were made at different times. 
The conclusion which we draw from all our observations is, that the coefficients of 
extinction of pure chlorine for chemical rays from various sources of hght are very 
different. The depth to which such light must penetrate chlorine at 0° and 0‘76, in 
order to be reduced to -j^th of its original intensity, is, according to the foregoing expe- 
riments, — 
(1) A flame .of coal-gas 173-0 millims. 
(2) Eeflected zenith light, morning . . 45-6 millims. 
(3) Reflected zenith light, evening . . . 19-7 millims. 
A variation in the same direction is also seen in the chemical extinction of the light. 
The depth to which the light must penetrate the normal chlorine mixture, supposing 
that no optical extinction took place, in order that the original amount of light should 
be reduced to i^th by the chemical effect produced, is — 
(1) A coal-gas flame 723-0 milhms. 
(2) Morning light reflected from a cloudless zenith . . 377-3 millims. 
It is thus seen that the chemical rays reflected at different times of the year, and at 
various hours of the day, not only possess quantitative but also qualitative differences, 
representing the various coloured rays of the visible spectrum. Had nature endowed 
our eyes with the power of discriminating the various degrees of refrangibility of the 
chemical rays, as she has done for the visible rays by impressions of different colours, 
we should see the rosy tints of morning pass in the course of the day through all the 
gi-adations of colour until the warm evening tones at length succeed. 
A long-continued series of observations must be made before we are able to under- 
stand the influence which these qualitative differences in the chemical rays exert in the 
