92 J. W. Draper—Distribution of 
From this it follows that on its passage through a mixture of 
chlorine and hydrogen, the radiation had sutfered absorption, 
and as respects the mixture under trial had become de-actinized, 
Simultaneously the mixture itself had been affected, its constit- 
uent gases uniting. And thus it appears that the radiation 
had undergone a change in producing a change in the pondera- 
ble matter. 
The following modification of this experiment shows the 
part played by the chlorine and hydrogen respectively, when 
they are in the act of uniting. 
a) The glass absorption vessel above described was filled 
with atmospheric air, and the chemical force of the radiation 
passing from the Jamp through it was determined. It was 
measured by the time required to cause the index of the actino- 
meter to descend through one division. This was 12 seconds. 
(6) The absorption vessel was now half filled with chlorine, 
obtained from hydrochloric acid and peroxide of manganese. 
than in the preceding case, since the chlorine was now uniting 
with the Paice On measuring the force it was found to be 
represented by 19 seconds. 
(d) Lastly, the first (a) of these measures was repeated with 
a view of ascertaining whether the intensity of the lamp had 
changed. It gave 12 seconds as before. j 
From these observations it may be concluded that the addi- 
tion of hydrogen to chlorine does not increase its absorptive 
wer. Moreover, it is obvious that the action of the radiation 
is expended primarily on the chlorine, giving it a disposition to 
unite with the hydrogen, and that the functions discharged by 
the chlorine and by the hydrogen respectively are altogether 
different. The ray itself also undergoes a change; it suffers 
absorption and loss of a part of its vis viva. 
As to the ray which is thus absorbed. In 1885 I found that 
a radiation which had passed through a solution of potassium 
bichromate failed to accomplish the union of chlorine and 
hydrogen; but one which had passed through ammonia 
phate of copper could do it energetically. This indicates that 
the effective rays are among the more refrangible. On expos- 
ing these gases in the spectrum, the maximum action takes 
place in the indigo rays (Phil. Mag., Dec., 18438). 
Recently (1871) some suggestions have been made by M. 
Budde respecting the action of light upon chlorine. Admit- 
