and the Absorption of the Tithonic Rays, 4-75 



added, the vessel being consequently full of the united mix- 

 ture. The force of the ray was again measured, and found 

 to be represented by 19 seconds. 



Lastly, the first of the preceding experiments was made 

 again, with a view of ascertaining whether the intensity of the 

 lamp had declined, or the apparatus remained in its former 

 condition. It gave again 12 seconds. 



Let us group these four results together, representing thus 

 the intensity of the beam by the time it requires to produce a 

 given effect. 



A beam through the glass vessel and atmospheric air 12 seconds 



chlorine 25'6 ... 



... ... chlorine and hydrogen... 19 



atmospheric air 12 



We therefore gather from this, that the addition of hydro- 

 gen to the chlorine, far from increasing its absorptive power, 

 actually diminishes it; that in the case before us, when to a 

 given volume of chlorine an equal volume of hydrogen has 

 been added, the absorptive power is diminished to one-half. 



We further see that the action of the beam is expended 

 primarily on the chlorine, giving to it a disposition to go into 

 union with hydrogen, and that the functions discharged by 

 the chlorine and hydrogen are wholly different. 



The chemical forces of the ray are easily deduced from the 

 foregoing measures, in which the times are given, for it is ob- 

 vious they are inversely proportional to those times. 



*Ks atmospheric air exerts no absorptive action on the titho- 

 nic rays, the foregoing experiments give us the effect of chlo- 

 rine, and of chlorine and hydrogen, compared with a vacuum. 

 The absorptive action of the glasses being common to all the 

 experiments, may be left out of the final estimate. The dif- 

 ference of the resulting numbers 25'5 and 19, from the pro- 

 bable numbers 25"5 and 18-7, may be accounted for from the 

 disturbing causes which are encountered, such as the constant 

 solution of the chlorine by the salt water of the pneumatic 

 trough. 



When therefore a ray falls upon this changeable mixture 

 of chlorine and hydrogen, the primary action takes place upon 

 the chlorine, which becomes tithonized, or has a disposition 

 given to it to go into union with the hydrogen ; the latter gas 

 appears to be passive so far as the ray is concerned. In the 

 mean time the ray itself becomes changed, undergoing ab- 

 sorptive action and being detithonized. 



It is important that we should bear in mind this distinction 

 of the functions which chlorine and hydrogen respectively dis- 

 charge. The same thing occurs in the Daguerreotype, in 



