curves for a magnetizing force of =b 1300 

 gauss show for the hardened steel an energy 

 loss of 900,000 ergs per cycle. Tempering is 

 best effected by heating to 950° C. and quench- 

 ing in heavy oil. This treatment applied to 

 annealed specimens increases the Brinell 

 hardness number from 444 to 652 and makes 

 the microstructure finer grained. 



3. The structure of the helium atom. Irving 

 Langmuir; Physical Review, 17, 339-353, 

 March, 1921. 



ABSTRACT 



Helium atom models. — (1) Bohr's model is 

 unsatisfactory because it gives too great a 

 value for the ionizing potential and is not in 

 accord with some of the optical and mag- 

 netic properties of helium. Since the chem- 

 ical evidence suggests that each electron in 

 an atom has its own orbit, separated from the 

 other orbits but closely interrelated with them, 

 two new models are considered. (2) In the 

 double circle model the two electrons are as- 

 sumed to move in two circular orbits, separate 

 but parallel. This model, however, is unstable, 

 for the ionizing potential computed by apply- 

 ing the quantum theory, comes out negative. 

 Another objection to this model is that the 

 magnetic moment is not zero. (3) In the 

 semi-circular model each electron is assumed 

 to oscillate back and forth along an approxi- 

 mately semi-circular path in accordance with 

 classical mechanics, each being brought to 

 rest at each end of its path by the repulsion 

 of the other. Assuming the maximum angu- 

 lar momentum of each electron equal to h/27r 

 the absolute dimensions come out such as to 

 give a total energy 0.9618 times that of the 

 Bohr model, and the computed ionizing po- 

 tential, 25.62 volts, agrees closely with the 

 experimental value. The magnetic moment is 

 zero. 



