62 



A STUDY OF THE ABSORPTION SPECTRA. 

 TYSON ITE 



e/m 



JVeat25U. E. M. 



JVeat -188 



Nm at 25 



Nm at 188 



TV at 25 



N at -188 



A 5176. 



+ 2.49 (10) 7 

 1.01 (10)- 5 

 2.50 (10)- 5 

 4.05 (10)-' 3 

 1.00 (10)" 12 

 0.89 (10) 18 

 2.21 (10) 15 



A 5235. 



2.48 (10)' 

 3.28 (10)- 9 

 7.07 (10)- 

 1.32 (10)- 1S 

 2.85 (10)- 13 

 2.9 (10) M 

 6.25 (10)" 



From the above, then, N, the number of absorbing electrons increases 

 as the temperature is lowered. The number of absorbing electrons is very- 

 much smaller than the number of atoms present. Hallo 1 and others have 

 shown that only a small number of sodium atoms take part in the absorp- 

 tion of the two D lines. 



D 3 (Hallo) e a =7.5 (lO)" 8 N 0t = 3.3 (10) 14 



A(Gerst) e ] =2.1(10)-' N 0i =1.1 (10) 16 



; 5221.5 (Xenotine).... e J5 =5.43 (10)~ 8 7V 25 =3.34 (10) 13 



e- 188 = 9.68 (10)~ 8 N 188 = 5.96 (10) 13 



The index of refraction of solids, and especially minerals, changes very 

 little with change in temperature, so that the electrons influencing refrac- 

 tion are but slightly affected by changes in temperature. Drude, Cheve- 

 neau, 2 and others have shown that the number of these electrons vibrating 

 in the ultra-violet is approximately that of the valencies of the atoms 

 composing the molecule. 



Becquerel 3 has continued his work at low temperatures, doing part 

 of the work with Onnes 4 at Leyden. One of the problems arising from 

 Becquerel's work is whether the paramagnetism of erbium and neodymium 

 affects the internal magnetic fields which would exist within the crystals 

 if they were diamagnetic. For this reason the Zeeman effect is found for 

 widely different temperatures. If the Zeeman effect is independent of 

 temperature then one would consider that paramagnetism did not play a 

 very important role. Becquerel finds the Zeeman effect on the bands of 

 xenotine and tysonite to be independent of the temperature. 



In a table giving the Zeeman effect on tysonite and parisite it is seen 

 that bands that are in practically the same portion of the spectrum are 

 affected in a very different way by the magnetic field. From the Zeeman 

 effect the following erbium alcohol bands are due respectively: X 4870 to ; 

 X 4880 to - ; X 5238 to + ; and X 5410 to - electrons. 



Considerable data are given by Becquerel upon the rotatory magnetic 

 polarization. The results confirm the theory of the Hall effect that the 

 sense of the dispersion is just the opposite on the outside of the band from 

 what it is on the inside. Applying the theory to the band X 5221.5 of 

 xenotine, Becquerel obtains the results shown in the following table: 



1 Arch. Neerlandaises (2), t. 10, p. 148 (1905). 



2 Le Radium, June (1907). 



3 Ibid., Jan. (1908); Nov. (1909); Compt. rend., Dec. 9, 30 (1907). 

 'Ibid., Aug. (1908). 



