Probable Normal State of the Helium Atom. 123 



regular crystalline structure cannot produce any dissipation 

 of energy during oscillations, it is to be understood why 

 annealing results in the diminution o£ the viscosity. In the 

 case of: copper, it is well known that annealing at about 

 300° C. produces a marked softening, or its plasticity and 

 hence the viscosity is increased by annealing. 



In carbon steels the coefficient of viscosity increases with 

 the content of carbon ; a small fluctuation from this law is 

 probably to be attributed to the presence of other impurities, 

 as seen by comparing the tw T o sets of curves in PI. IV. fig. 2. 



Summary. 



1. The coefficients of normal viscosity of 12 different 

 metals are measured at room temperature; their values range 

 from 0-7 x 10 s to 27 X 10 8 . 



2. The coefficient of the viscosity of a metal having a low 

 melting-point is large. 



3. The coefficient of normal viscosity is of the same order 

 of magnitude as that of tangential viscosity. 



4. Annealing causes the diminution of the coefficient of 

 viscosity. 



5. In carbon steels the coefficient of viscosity increases 

 with the content of carbon. 



VIII. The Probable Normal State of the Helium Atom. 

 By Edwin C. Kemble *. 



Introduction. 

 HPHE quantum theory of the origin of the line spectra of 

 ~L gases conceives of each of the " terms " whose combi- 

 nations give the frequencies of the spectrum lines as the 

 measure of the energy of one of the possible stationary states 

 of the atom. The emission of radiation accompanies the 

 passage of the atom from one to another of these stationary 

 states, which differ primarily in the nature of the corre- 

 sponding orbits of the outer electron. Each of these orbits 

 is characterized by an azimuthal quantum number which 

 specifies its angular momentum, and a radial quantum 

 number. The azimuthal quantum number is believed to 

 be unity for the orbits corresponding to the sharp series 

 terms, two for the principal series, three for the diffuse 

 series, and so on f . 



* Communicated by Prof. Theodore Lyman. 



f A. Sommerfeld, Atombau wad Spektrallimen, 2nd edition, Braun- 

 schweig 1 , 1921, p. 278. 



