278 MODIFIED CHLORINE. [MEMOIR XIX. 



liquid in a graduated tube; and from this we gain just- 

 er views of the true constitution of the spectrum. On 

 studying the numbers in the foregoing table, or, better 

 still, if we project them, it will appear what an enormous 

 difference there is in the chemical force of the different 

 rays. In the experiment from which I have deduced 

 this table it appears that the force of the indigo ray 

 exceeds that of the orange in a greater ratio than 66 to 

 1 ; and from the circumstances under which the experi- 

 ment is made this difference must be greatly underrated. 

 There is always diffused light in the room coming from 

 the intromitted beam, and this accelerates the rise in the 

 less refrangible tubes ; then, again, it is impossible that 

 the tube which gives the greatest elevation shall coin- 

 cide mathematically with the maximum point and ex- 

 press the maximum effect. 



From some estimates I have made I am led to believe 

 that in point of chemical force, for this mixture of chlo- 

 rine and hydrogen, the indigo ray exceeds the red in a 

 higher ratio than 500 to 1. 



VI. The Action is Positive from Mid to End of the 



Spectrum. 



M. Becquerel found that for an iodized silver plate the 

 red, the orange, and the yellow rays possess the quality 

 of continuing the action begun by the more refrangible 

 colors ; he therefore names these " rayons continuateurs? 

 For the same compound I found that those rays, acting 

 conjointly with the diffused daylight, exerted a negative 

 agency. It is therefore desirable to understand whether, 

 with respect to the gases now under consideration, the 

 less refrangible rays exert anything in the way of an ac- 

 tion of depression or hindrance to union. By direct ex- 

 periment I found that this was not the case, the action 

 being positive from end to end of the spectrum. This 



