﻿228 Prof. E. C. 0. Baly on 



spectra. This, however, cannot be entered into here. It is 

 sufficient to say that it does not seem probable that there is 

 any especial significance in the band heads in the absorption 

 spectrum, and further that the whole oi the remainder of 

 the absorption bands of benzene beyond those given in the 

 table may arise from a combination of the rotational fre- 

 quencies of the molecules with the frequencies given in the 

 table. These rotational frequencies certainly are of the 

 right order of magnitude. 



Turning now to the frequency of the central line 4055, it 

 follows, if the deductions in the previous paper are sound, 

 that this must be a whole multiple of the frequency of one 

 of the infra-red bands. It is almost exactly 10 x 405*, which 

 corresponds to a wave-length of 2*47 fi, which corresponds 

 to the band observed by Coblentz at 2*49 fj,. Now the next 

 multiple of 405 is 9x405 = 3645, and this should form the 

 central line of the fluorescence bands of benzene. The 

 fluorescence of an alcoholic solution of benzene has accurately 

 been measured bv Dickson t, who found 6 bands with fre- 

 quencies of 3436, 3537, 3631, 3733, 3795, and 3848. Now 

 in order to compare these with the absorption measurements 

 they must be corrected for the effect of the solvent which 

 tends to shift the maxima towards the red. The values must 

 therefore be increased by a few units. If 14 be added to 

 the third frequency w T e have 3645, which should be the 

 central line of the system. It may be assumed, therefore, 

 that 14 should be added to all the values, and this is done in 

 the third column of Table III. In the fourth column are 

 given the frequency differences from the central line 3645 r 

 and in brackets are the mean values for the corresponding 

 intervals found in Table II. 



Table III. — Benzene fluorescence (Dickson). 



o X in 

 Angstroms. 



1/X. 



1/X + 14. 



„ 1 



2910 



3436 



3450 



195 (194) 



2827 



3537 



3551 



94 (92) 



2754 



3631 



3645 







2679 



3733 



3747 



102 (101) 



2635 



3795 



3809 



164 (160) 



2599 



3848 



3862 



217 (208) 



The agreement is remarkably good. 



* The reason why this number is selected will be dealt with in a 

 further communication. 



t Zeit. iciss. Phot. x. p. 1G6 (1912). 



