Absorption and Fluorescence. 419 



In the sixth and seventh columns are shown the wave-lengths 

 of the infra-red bands as observed by Coblentz * and by 

 8 pence f. 



Table II. 











Infra-red Bands. 



X. 



1/X. 



v r . 



Mean 



V 





















*>■ 



Gale. 



Obs. 

 Coblentz. 



Obs. 

 Spence. 



2930 



3413 



174 



. 



575 n 



5-80 fi 





2918 



3427 



160 





6-25 



625 



6-35 ft 



2908 



3439 



148 



147-5 



6-79 



675 





2892 



3458 



129 



129-5 



7-72 



775 





2879 



3473-5 



113-5 





8-81 



8-78 



8-80 



2872 



3482 



105 





9 52 



9-85 



950 



2869 



3486 



101 





9-90 



973 



977 



2866 



3489 



98 



9875 



10-13 



10-08 



10-15 



2861 



3495 



92 



92 



10-87 



10-85 





2860 



3497 



90 





11-11 



11-28 





2855 



3503 



84 



si" 



11-90 



11-90 





2789 



3587 















2730 



3663 



76 





1316 



13-3 





2726 



3668 



81 





12-35 



12-4 





2724 



3671 



84 



84" 



11-90 



11-90 





2718 



3679 



92 



92 



10-87 



10-85 





2712-5 



3686-5 



99-5 



98-75 



10-13 



10-08 



10-15 



2696 



3709 



122 



... 



10-32 



10-53 





2690 



3717 



130 



129-5 



7-72 



7-75 





2685 



3724 



137 





7-30 



7-30 





2681 



3730 



143 





6-97 



695 



6-95 



2678 



3734 



147 



147-5 



679 



6-75 





It may be seen that the agreement between the calculated 

 and observed values is exceedingly good. It is an inter- 

 esting fact that the absorption-band group as observed for 

 pyridine vapour is not the same as for that observed with a 

 solution of pyridine, for the centre of the former is at 

 l/\=3587, while the centre of the latter in dilute solution, 

 as shown in Table L, is about 1/X = 3910. This fact has 

 already been noted by Purvis, and is of some value in the 

 present connexion because it enables us to determine whether 

 the relation between the wave-numbers of the centres of 

 two absorption-band groups holds good. Now the difference 

 between the above values of 1/X for the two absorption 

 t>ands is 323, and therefore this must be very nearly the 

 fundamental infra-red wave-number of pyridine. 



Since the value of l/\ — 3587 may be taken as an 



* Publications of the Carnegie Institution, Washington, No. 35 (1905). 

 1" Astrophvs. Journ. xxxix. p. 243 (1914). 



2 F 2 



