CONTEMPORARY ADVANCES IN PHYSICS 



677 



(I pause to point out the relation between formula (8) and the earlier 

 formula (1). The first two terms in the Taylor expansion of e~y being 

 (1 — 3*), one may write instead of (8), 



<2 = <2o - Q^Nax, (10) 



which is formula (1).) 



The experiment of Ramsauer acquired instant fame, because the 

 data which he got with argon were of a nature totally unexpected,^" and 

 caused immense surprise. 



His apparatus is a metal box, partitioned into chambers, the party- 

 walls of which are pierced with slits delimiting a narrow path curved in 

 the form of a circle. Details are different in the different boxes which 

 he used at various times, and in those which several other physicists — 



CM 



5r- 



Fig. 2 — Ramsauer's apparatus for measuring the cross-section for interception. 



{Physikal. Zeitschrifl.) 



Maxwell, Erode, and T. J. Jones among them — made after the pattern 

 of his; but a fair idea of all is given by Fig. 2. Photoelectrons ^^ escape 

 from the metal plate at Z, and are accelerated to the speed desired by a 

 potential-rise from Z to the walls of the box. The electron-beam con- 

 sists of corpuscles sweeping around in circles so centred and so propor- 

 tioned that they pass through all the slits. It is of course a magnetic 



^^ This was first disclosed in Mayer's paper from the same laboratory, but Mayer 

 yields to Ramsauer the credit of having noticed it sooner. 



11 Some of the American physicists used thermionic electrons instead; in certain 

 experiments the filament replacing Z is encased in a coaxial cylinder with a narrow 

 slit, from which electrons escape after receiving the energy corresponding to the po- 

 tential-rise from filament to cylinder. 



