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BELL SYSTEM TECHNICAL JOURNAL 



will be as many different electron-speeds represented in the emerging 

 electron-stream as there are levels,' and from these speeds the extrac- 

 tion-energies characterizing (or indeed defining) the levels can be 

 deduced. 



The apparatus in which the test is made is of the type shown in 

 Fig. 1. At 5 there is a long narrow rod or tube of the material being 

 tested, irradiated by X-rays proceeding from a source at the left. A 

 magnetic field, directed normally to the plane of the paper, sweeps 



Fig. 2 



the emerging electrons around in circular arcs, some of which pass 

 through the slit; a few such arcs are sketchetl. The slower the electron, 

 the more highly curved the path in which it travels; and the speed 

 of the electron can be deduced from the curvature of the path. In 

 P'ig. 2 electron-paths of this type are reproduced from a photographic 

 film, which was laid parallel to the plane of the paper, in the posi- 

 tion of the rectangle marked I in Fig. 1. Fig. 3 shows arcs which 

 appeared on a film laid in the position of the rectangle marked II. 



' Of course there may be reasons why electrons in particular positions cannot 

 often or at ail be extracted by radiation, even though there is plenty of energy 

 available. 



