Temperature Radiation of Gases. 275 



conditions and gradually increase as the temperature is 

 raised or the concentration is lowered. As an example, we 

 TZft^M ^tribution of the Ca atoms in the orbits 



at 000 11 follow according to the scheme (we are considering 

 only f here) to 



(i- T V)[i, io- 1 , ]o- 2 , io- 3 ....], 



while at 4000° K, the distribution is 



so that the relative intensity of the lines 



(l,s)-(2,p), (2,p)-Q\,d), (3,rf)-(4,6) 



will be 1 : 10-i : 10" 2 , etc. ; 



b kV 111 ! 7 ! ?n°no P -? °, ent " ° f the at0ms wiI1 remain inactive, 

 while at 4000° K, the ratio will be 



!':*:( 



i)\ 



bat now only 25 per cent, of the non-ionized atoms remain 

 inactive. 



The above considerations are not based upon any theoretical 

 argument but are given here as a sort of construibar vor- 

 steltung ot the statistics of line-radiation of gases. We can 

 say that under all physical conditions, a very small concen- 

 tration ot radiant atoms suffices for the production of the 

 series „=(1, s ) — (m,p), especially the fundamental line 

 v = (l,s)-{2,p). /The (2,p)~( m ,ck), (2, ,) -(m,p), (3, d) 

 -(m, J) lines require gradually increasing concentrations of 

 radiant matter in addition to the condition that the stimulus 

 should be sufficiently great. For example, if we take 

 sodium gas at a temperature of 1500° K [an ordinary Bunsen 

 flame tinged with sodium vapour], and gradually decrease 

 the amount ot vapour in the name, the order in which the 

 lines disappear are (3,<9-(m,&), (2 9 s)-(m,p), (2,p) 

 ~(m d) ; the (1,,)-( W ,jO lines, of which the leadino- 

 members are the D, and the D 2 , are the last to disappear, a 

 fact which was recognized by Du Gramont, when lie con- 

 ferred the appellation "rates ultimes" upon this class of lines*. 

 inis state ot affairs persists when the temperature is raised 

 and gradually increasing percentages of atoms are ionized. 

 It a line is represented by the series formula v=( ii: f)-( n' } f), 



* According to Bunsen and Kirchhoif, 7x10"" gm. of sodium in the 

 Bunsen flame is quite sufficient to show the 1), and the D a line 

 {1 rmgsheim, Physik der Sonne, p. 121). 



T2 



