[MCLENNAN- young-ireton] ABSORPTION SPECTRA 9 



In addition to the above, absorptions were recorded at 3230 A.U, 

 and 2530 A.U., the latter Hne not yet assigned to any series. No 

 absorption was found at 3776 A.U. which would indicate that the 

 presence of mercury is necessary for this absorption. Two of the 

 sixteen series lines have not previously been recorded. They are 

 2065 A.U. and 2059 A.U. belonging to the series v= (2,p2) -(m,s). 



The reproduction in Plate I illustrates the nature of the absorp- 

 tion obtained with thallium vapour. Attempts were made to obtain 

 absorption at 1700 A.U. with thallium salts in the carbon arc in 

 vacuo with the fîuorite spectrograph, but these have been up to the 

 present unsuccessful. This may be due to the difificulty in producing 

 dense enough vapours in vacuum arcs which were open to the pumps. 



IV. Absorption Spectrum of Aluminium 



In case of aluminium it was found impossible to use any of the 

 salts owing to the formation of the oxide which was irreducible in 

 the arc, so that the metal itself was used. No absorption was ob- 

 served visua.lly with a small glass spectroscope but the spectrograms 

 revealed series of absorption bands in the ultra violet. When care- 

 fully measured it was found that the values agreed exactly with those 

 given by Dunz^ for the series i; = (2,p2) — (m,d'} and v= (2,p2) — (m,s). 



In the former series nine absorption bands were found and in the 

 latter, five. They were as follows: 



Since no other absorptions were observed, no new series relations 

 can be predicted from the work, but it is of interest to note that 

 the frequencies 



v=(2,p2)-(12,d0, v=(2,p2)-(13,d') 

 i;=(2,p2)-(14,dO, v = (2,p2)-(6.5,s) and 

 y=(2,p2) — (7-5,s) have been recorded for the first time. 

 The reproduction shewn in Plate II is that of the absorption 

 spectrum of aluminium. 



' Dunz, loc. cit. 



Sec. Ill, Sig. 2 



