4O2 TABLE 515 (continued). 



BOHR ATOM. MAGNETIC FIELD OF ATOM- 



being determined by kv = Ai At, h being Planck's constant and A\ and At. the energies in the two orbits; (c) the 

 various possible circular orbits, for the case of a single electron rotating around a single positive nucleus, to be deter- 

 mined by T = (i/2)rhn, in which r is a whole number, n is the orbital frequency, and T is the kinetic energy of rotation. 



The remarkable test of this theory is not its agreement with the H series, which it was constructed to fit, but in the 

 value found for N. From (a), (b), and (c) it follows that N = (2T^e t E 2 m)/h 3 = 3-294 X lo 15 , within i/io per cent of 

 the observed value (Science, 45, p. 327). 



The radii of the stable orbits = TW/4ir*me*, or the radii bear the ratios i, 4, 9, 16, 25. If normal H be assumed to be 

 with its electron in the inmost orbit, then 20. = i.i X io~ 8 ; best determination gives 2.2 X io~ 8 . The fact that H 

 emits its characteristic radiations only when ionized favors the theory that the emission process is a settling down to 

 normal condition through a series of possible intermediate states, i.e., a change of orbit is necessary for radiation. That 

 in the stars there are 33 lines in the Balmer series, while in the laboratory we never get more than 12, is easily explica- 

 ble from the Bohr theory. 



Bohr's theory leads to the relationship v% v% = V L ( see x ' ra y tables) , Rydberg-Schuster law. 



/8 a a 



For further development, see Sommerfeld, Ann. d. Phys. 51, i, 1916, Paschen, Ann. d. Phys., October, 1916; 

 Harkins, Recent work on the structure of the atom, J. Am. Ch. Soc. 37, p. 1396, 1915; 39, p. 856, 1916. 



Magnetic field of atom : From the Zeeman effect due to the action of a magnetic field on the radiating electron the 

 strength of the atomic magnetic field comes out about ip 8 gauss, 2000 times the most intense field yet obtained by an 

 electromagnet. A similar result is given by the rotation of a number of electrons, Aio 3 , where A is the atomic 

 weight; for Fe this gives io 8 gauss. For other determinations, see Weiss (J. de Phys. 6, p. 661, 1907; 7, p. 249, 1908), 

 Ritz (Ann. d. phys. 25, p. 660, 1908), Oxley (change of magnetic susceptibility on crystallization, Phil. Tr. Roy. Soc. 

 215, p. 95, 1915) and Merritt (fluorescence, 1915); Humphreys, "The Magnetic Field of an Atom," Science, 46, p. 276, 

 1917- 



SMITHSONIAN TABLES. 



