1889.] Absorption- Spectra of Oxygen and its Compounds. 227 



trace no identity between the absorptions of ozone and those of 

 ordinary oxygen. There is no mere displacement of the bands, such 

 as we sometimes get when a coloured substance is dissolved in 

 different menstrua, nor any such a resemblance as we have between 

 the absorption-bands of the different cobaltous salts derived from 

 different acids. 



The four bands which we see- to be produced by ozonised oxygen 

 correspond fairly with the 2nd, 3rd, 5th, and 6th of the bands 

 described by Chappuis as due to ozone (' Annales de l'Ecole Nbrmale,' 

 2nd ser., vol. 11, May, 1882). These four bands, he says, are the first 

 to be seen. We have failed to perceive any others with the 3"66 m. 

 tube, though the oxygen was highly ozonised and maintained at a low 

 temperature. None of the bands were of sufficient intensity to make 

 themselves visible on our photographic plates. 



It will be noted that the absorption by ozone extends far below the 

 limit of the solar spectrum. We found, however, that by diminish- 

 ing the proportion of ozone to oxygen in the tube the limit of the 

 transmitted light was continually advanced, as already described by 

 Hartley. The limit of the solar spectrum may, therefore, very well 

 be determined by the average amount of ozone in the atmosphere, as 

 Hartley supposes. The known variations in the limit of the solar 

 spectrum may be taken as confirmatory of this hypothesis, although 

 the comparatively small amount of those variations is certainly less 

 than we should have expected if they measure the changes in the 

 proportion of ozone in the atmosphere. 



The absorptions of the class to which A and B belong must be 

 those which are most easily assumed by the diatomic molecules (O 2 ) 

 of ordinary oxygen. Whether oxygen in more complex molecules, as 

 in ozone (O 3 ), may be capable of taking up the corresponding vibra- 

 tions cannot easily be determined because we cannot isolate ozone ; 

 but since none of the compounds of oxygen with nitrogen, hydrogen 

 or carbon, or, so far as known, with any other element, exhibit these 

 absorptions, it is very probable that they are peculiar to the molecule 

 O 2 . From this point of view it will be interesting to determine — as 

 we hope to do shortly — whether liquefied oxygen, which we suppose 

 to have more complex molecules, produces these absorptions. The 

 corresponding spectrum of emission has not as yet been observed, 

 probably because the agency employed tP render the gas luminous 

 breaks up the molecules into single atoms of oxygen. 



As for the other class of absorption, the diffuse bands, since they 

 appear to have intensities proportional to the square of the density of 

 the gas, they must depend on a change produced by compression. 

 This may either be the formation of more complex molecules, as for 

 example O 4 , corresponding to the deviation from Boyle's law ex- 

 hibited by oxygen gas, or it may be the constraint to which the 



