682 BELL SYSTEM TECHNICAL JOURNAL 



For helium and neon, on the other hand, the cross-sections vary 

 but Httle over the energy-range from 1 to 40 equivalent volts, though 

 for each there is a gentle flattish maximum. Below one equivalent 

 volt, <j for neon falls gradually and smoothly as far as the limit (0.16 

 e.v.) of Ramsauer and Kollath's data, while the curve for helium 

 has a couple of wiggles. Normand and Erode find a minimum in the 

 neon curve. 



It seems odd to speak of methane (CH4) among the monatomic 

 gases; but its a-curve is of the same kind as those of the three mas- 

 sive noble gases, displaying a sharp maximum ^^ near 8 equivalent 

 volts. One notices however that if the four electrons of the four H 

 atoms were to join the four outer electrons of the C atom, they could 

 form a shell of eight to simulate the closed outer shell of an inert-gas 

 atoms. But the noble gas most closely simulated should be neon, and 

 neon does not show the high sharp maximum. 



The other monatomic gases are the vapors of the metals. As in the 

 measurements of their resonance and ionizing potentials, they are 

 difficult to handle. There is an extra difficulty, over and above those 

 which beset the seeker after critical potentials: the measurer of a must 

 know the density of the gas, therefore the vapor-pressure of the metal 

 with which he is working. But vapor-pressures change so rapidly 

 with the temperature, that this must be determined very carefully. 

 Even after one has determined the temperature with exceeding care, 

 one may find on searching the literature that the density-vs-tempera- 

 ture curve has never been reliably determined. The data for mercury 

 are by far the most abundant; there are a few for cadmium and zinc, 

 which belong to the same column of the periodic table (Fig. 6). All 

 three have similar cross-section curves, which except for a little hump 

 near 40 equivalent volts rise steadily with fall of corpuscle-speed. I 

 reproduce an additional curve for mercury (Fig. 7), for it illustrates the 

 smallness of the difference between the <j of the Ramsauer method and 

 that of the method of Mayer. The "method of Part I " is substantially 

 Ramsauer 's; the "method of Part II" involved the use of the tube 

 shown in Fig. 3. 



The four familiar members of the alkali-metal column were subjected 



to experiment by Brode; each of the four curves of A^^icr versus electron- 



, energy has a sharp maximum near 1 or 2 equivalent volts, and this 



maximum is astonishingly high — greater than 1000 for all four, almost 



1^ R. B. Brode (P. R. (2), 25, 636-644; 1925). Akesson is said to have discovered 

 this maximum, even before Ramsauer's research {Lund Arsskrift, 1916). This paper 

 of Akesson's is the outstanding example of an article which hundreds cite for one who 

 has seen it. For some reason — the war, very likely — -it was never published in any 

 journal enjoying a wide circulation. 



