276 



Dr. Megh Xad Saba on the Problems of 



the difficulty of detection of the line- will be greater the 

 larger are the values of n and n' . 



In the following table we give the temperature of complete 

 ionization of a few elements, with the temperatures at which 

 luminescence just begins and attains its maximum intensity. 

 But it will be clear from what has been said that the ordinary 

 way of speaking— " the gas is heated to incandescence or 

 luminescence just begins" — has no meaning in itself unless 

 we say which particular line is emitted, or which orbit is 

 produced. The orbits which are produced are specified in 

 column 3. Under the heading "•■ Remarks," the manner in 

 which these temperatures have been estimated are briefly 

 described. In this connexion, the following section on 

 absorption should be consulted. The pressure has been 

 taken equal to one atmosphere unless otherwise stated. 



Table III. 



Element. 



II 



He. . 



Mg + 



Ca] 



Sr 

 Ba 



Temperature 



of 



Ionization. 



24.000 



32.000 



24,000 



10,000- 



8000° K 



(Pressure 



10- 1 atm.) 



Orbit 



, -, escence 

 generated, 



Remarks. 



Lumin- 

 escence is 

 maximum 

 at 



(2, p) I 5000° K 



Temp, of I lf , 000 o K 

 Ma stars 



(2,p) I 11.000° K T 4 e ,f P" of 17.000° K 

 v J ' \ AZ class 



(3, d) j 7500° K ^ em ],L of 11,000° K 



(2, p) \ 1500° K 



Go class 



Bunsen 



flam 



4000 



Remarks. 



Temp, of 

 Ao stars 



Temp, of 

 B2A class 



Temp, of 

 A2F class 



The open 

 arc 



The elements N 2 , 2 , A, Ne, etc., resemble H 2 and He in 

 having large values for the ionization-potential, and therefore 

 they fail to respond to the temperatures which can be com- 

 manded in the laboratory. The alkali metals (particularly 

 K, Rb, Cs) are more prominent in the flame-spectra and less 

 in the arc than the alkaline earths. Mg- lines are rather faint 

 in the flame, but come out very prominently in the open arc. 

 Zn, Cd, rig, Fe, Ti lie between the alkaline earths and the 

 permanent gases in their spectral properties. All this is 

 in very good qualitative agreement with the hypothesis 

 sketched in the present paper. 



