680 BELL SYSTEM TECHNICAL JOURNAL 



suffered much loss in speed but little deviation,^'' and the a measured by 

 the so-modified device would approach more nearly to that of Ram- 

 sauer's. Modifications like this might conceivably entail enormous 

 changes of the relevant cross-section. But it happens that they do not 

 — a very important fact " in itself, illustrated by Fig. 7 (for mercury 

 vapor) ; and therefore the results of all the work can be summarized 

 en bloc. 



I begin with the surprising fact, of which the disclosure excited so 

 wide an interest in this field. Argon was the gas on which the dis- 



150 



A XENON 

 o KRYPTON 

 • ARGON 



1234 56789 10 



/VOLT 



Fig. 4 — Cross-sections of atoms of three of the noble gases, determined by Ramsauer 

 with the scheme of Figure 2. (Physikal. Zeitschtift.) 



covery was made by Ramsauer, and checked by Mayer (and a little 

 later by Townsend and Bailey, in an entirely different way; but since 

 krypton and xenon show even more strikingly the "anomaly" — 

 as it used to be called, and should be called no longer — I present the 

 curves for all three of these gases together (Fig. 4). They are curves 

 of Ni<j (the reciprocal of Zi) versus the speed of the electrons. ^^ 



^^ This in effect was done by Mayer, whose collector was shaped like a cup covered 

 over with a pair of parallel gauzes; he made the cup and the inner grid a volt or two 

 more negative than the outer gauze. Notice that this is a scheme for detecting crit- 

 ical potentials for onset of inelastic impacts. 



1** Moreover, a distinctly puzzling fact, especially as sometimes the o- obtained 

 by Ramsauer's method appears to be less than that obtained by Mayer's (see Fig. 7, 

 and the paper of M. C. Green). 



1^ In this department of electronics it is the custom to use as independent variable, 

 not the kinetic energy of the electrons expressed in equivalent volts, but the speed of 

 these corpuscles expressed either in centimetres-per-second, or (more commonly) in 

 "square-roots-of-equivalent-volts," i.e. in a unit equal to 5.94- 10' cm. /sec. I do not 

 know of any valid reason for this anomaly of usage, except insofar as it may be found 

 that the corresponding curves for protons and other ions display similar features at 

 equal speeds but not at equal energy-values. 



