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BELL SYSTEM TECHNICAL JOURNAL 



sees the traces on the plane of the paper, and go on to the annular 

 collector X; those which are deflected through other angles are caught 

 by the rings. A potential-drop from the rings to the annular collector 

 precludes from reaching this the electrons which in being scattered 

 have lost more than 15 per cent of their initial energy, so that the 

 ratio of the currents to K and ^ is a measure of the proportion of the 



I 



Fig. 12 — Kollath's apparatus for determining amount of scattering at angles near 90° 



{Annalen d. Physik.) 



primary electrons, which in traversing a (known) distance through gas 

 of a (known) density are deflected without more than the stated loss of 

 energy through angles within 3° of a right angle. Measuring the ratio 

 at various pressures of gas, Kollath determined the corresponding 

 cross-section for a number of gases. The continuous curves of Fig. 

 13 are those which he obtained for three of them; the broken curves 

 represent the intercepting cross-section as found by Ramsauer, with 

 ordinates reduced in the ratio 1 : 20. One sees that for each gas the two 

 cross-sections vary in much but not altogether the same way.^^ 



I must quote the results of the work of Langmuir and Jones, though 



1' It happens that the ratio 1 : 20 is about the ratio which the electrons received 

 by the collector K would bear to all the scattered electrons, if the distribution-in- 

 angle of these were isotropic — which of course is not necessarily so. 



