SOM/l CON'I'IIMPOR.IR)- ,l/)}\lNCi:S JX J'llVSlCS—XI 4S1 



(liciti'd by the characlerislic X-rci\-s of tungsten.'" To guard against 

 the possibility that the photograjihs ma\' lose in clearness 1)\- the proc- 

 ess of reproduction, I will base the explanation upon the uppermost of 

 the sketches in Fig. 7, which is abstracted by de Broglie from similar 

 pictures. The electron-speeds corresponding to the lines increase from 

 left to right. The irradiating X-rays consist of four characteristic fre- 

 quencies from the X-ray spectrum of tungsten ; in order of decreasing 

 frequency they are known as Ky, K0, and the two members of the Ka 

 doublet. The four lines marked 4 and 5 in the electronic spectrum are 

 made by electrons extracted by these four radiations from a single level 

 — the K level of the silver atoms. The two following doublets, marked 

 6 and 7, are made by electrons extracted by the Ka frequencies from 

 two other levels of the silver atom, the L and M levels respectively. 

 Line 8 is due to KfS extracting electrons from the L level. At the other 

 end of the spectrum, the three lines 1, 2, 3 are due to electrons ejected 

 from the L and the M levels by two of the X-ray frequencies character- 

 istic of silver, which the irradiating X-rays stimulate some of the silver 

 atoms to emit. The rays responsible for these particular lines are the 

 so-called Ka and K0 rays of silver, which are so related to one another 

 (as will be stressed in a later passage) that the electrons extracted by 

 the former from the M level have very nearly the same energy as the 

 electrons extracted by the latter from the L level, so that the two fre- 

 quencies acting on the two groups of electrons produce three (instead 

 of four) distinct lines of the electronic spectrum. 



Reverting now to the photographs: in Fig. 8 the pairs of lines 

 marked 4, 3, and 2 are those designated respectively as 6, 5 and 4 in the 

 sketch and in the foregoing explanation, while the lines to the left are 

 those produced by characteristic X-rays of silver acting upon silver 

 atoms. On a larger scale, this latter region of the spectrum is shown 

 in Fig. 9; here the lines are marked by the same numerals as in the 

 sketch ; the pair at 4 is due to X-electrons extracted by the two Ka rays 

 of tungsten, the line 3 is due to ilf-electrons extracted by the K^ radia- 

 tion of silver, the line 2 results jointly from L-electrons extracted by 

 the Kl3 radiation of silver and ilf-electrons expelled by the i^a-radiation 

 of silver, while the line 1 is due to L-electrons ejected by the Ka-rays 

 of sil'x'Cr. 



The resemblance and the differences between electronic spectra of 

 elements not far apart in the Procession are illustrated by the two 

 sketches in Fig. 7, the lower relating to tin (atomic number 50) and the 

 upper to silver (atomic number 47) irradiated by the same frequencies. 



" I am greatly indebted to M. de Broglie for sending me the negatives of these 

 admirable pictures, as well as that of Fig. 10. 



