Ultra-violet Absorption of Sulphur Dioxide. 511 



The differences between the calculated and observed values 

 in Tables IV., V., and VI. show how well the theory con- 

 forms to experiments. It should, moreover, be remembered 

 that the order of accuracy in infra-red measurements is 

 smaller than that in the ultra-violet regions. 



The whole gaseous absorption of sulphur dioxide can, 

 therefore, be analysed as follows : — 



Basis Constants: 0-2, 2*8 (oxygen), 4 (oxygen), 4 3 (sulphur). 

 Fundamental Frequency : (F) 02 X 2*8 X 4 X 4' 3 = 9'632. 

 Infra-red Spectrum : (F) xlO, 12, 14, 18, 26, and 32. 

 Centre of First Ultra-violet Band : (F) X 14x25. 

 Constant Wave-number Difference in First Ultra-violet Band : 



0-2x2-8x4x10. 

 Constant Wave-number Difference in Second Ultra-violet 



Band: 0-2x4x4'3xl0. 



I hope in later work to pursue this search for the basis 

 •constants characteristic of the elements. 



Reference may be made to Miss Lowater's analysis of the 

 •completely resolved ultra-violet absorption spectra of sulphur 

 dioxide, in which she determined the wave-lengths of all the 

 absorption lines composing the sub-groups of the whole band 

 groups *. Altogether 590 lines were measured by her, and 

 these were arranged in 44 arbitrary series with constant 

 wave-number differences. The mean of all these wave- 

 number differences was 22'3, which is practically identical 

 with that now found between the wave-numbers of the 

 centres of the sub-groups over the region dealt with by 

 Miss Lowater. Owing, however, to the great dispersion 

 used, she did not recognize the composite nature of the 

 spectrum dealt with above. Moreover, the intensity of her 

 lines was estimated by inspection on the conventional basis 

 of 10 for a very dark (absorbed) line. By such a method 

 it is impossible to estimate the persistenc}' of the lines, 

 and hence the real optical centre of the resolved complex 

 band system of the gas remained undiscovered. 



Finally, as the wave-number difference 34*4 characteristic 

 of the extreme ultra-violet region of absorption of sulphur 

 dioxide is derived from the specific sulphur bases, it may be 

 concluded that it is the sulphur atom of sulphur dioxide 

 which is mainly responsible for the production of this second 

 ultra-violet band group, a portion of which only has been 

 observed on account of the limited transparency of quartz. 

 By similar reasoning the oxygen atoms in the molecule must 

 be the chief determining cause of the typical band system 

 characteristic of the first absorption band group in the near 

 ultra-violet region. 



* Astrophys. Journal, xxxi. p. 311 (1910). 



