162 «/:7./. sySTEM TECHMCAL JOURXAL 



used to be supposcil. Imitaling de Broglie's term "spectres cor- 

 pusculaires" we ma\- ctill these "electronic spectra." But it must 

 be rcmemliered that tlie>- depend not onl\- on the iirojiertics of the 

 atom, but on the incident radiation as well. 



Maurice de Broglie has undertaken an exlensi\e stud>' of these 

 electronic spectra. His most recent apparatus, similar in general to 

 the arrangement illustrated in Fig. I (with the photograjihic plate 

 laid normalK" to the iilanc of the arcs) is impro\ed in various respects 

 and enlarged to permit of using a plate 24 cm. wide and electron-paths 

 of 26. cm. radius. InfortunateK', the ideal condition of atoms irradi- 

 ated b\- radiation of a single frecjuency, is unattainable. This is not 

 merel\- because actual X-ra\' sources emit \er\- mixed radiations 

 intense at several distinct frecjuencies and perceptible at e\er>- fre- 

 quency over a wide range. This difficulty could be partly remeilied 

 b\- appropriate filters. There is another difficulty and an inevitable 

 one; the atoms from which electrons are extracted by the radiation 

 promptly emit radiation of new frequencies, which extract other 

 electrons themseKes. In tin- language of the opening paragraph, the 

 arrangement of electrons which results when an electron is extracted 

 is not a permanent one: the remaining electrons redispose them- 

 sehi's in one arrangement aftc-r another, e\entually arri\-ing at the 

 permanent one; to each successiw arrangement corresponds a new 

 and lower value of the energy of the atom, and the energy -differences 

 \E are successively sent out in radiations of fretiuencies \E h. Thus 

 there are several freciuencits at work i-xtracting electrons from the 

 atoms; and in the electronic spertnim, larli le\el is represented 1)\- 

 as many lines as thiTc are tre(iuencies. 



The uppermost s|)ertrum ol I'ig. .") is sketched by dc Hroglir Ironi 

 photograi^hs made with the electrons emitted by silver atoms irradi- 

 ated with the characteristic X-rays of tungsten.-' The electron-speeds 

 corresponding to llii' lines increase from left to right. There are 

 four of these tungsten ra\>. luo forming the Ka doublet, while the 

 other two, known as Kji and Kb, ha\e higher fretiuencies. The foiu' 

 lines marked 4 and o in the electronic spectnnn are matle by electrons 

 extracted b>' these four radiations from a singk' lexel. This is the 

 A'-le\el, the deepest or innermost lr\ il in the .--iKer .itoni. the elec- 

 trons removed from it having lost more energy during the remo\al, 

 than an>- others observed, — about :i.4(V10 " ergs apiece. The two 

 following doublets, marked li and 7. ,nc nia<lc b\- eU-ctrons extracted 

 by the Ka frequencies from Iwd <lislincl lc\il> of tlu' silver atom, 



= S()im- pholonriiphs iiiiiv Ik- M'um in the Jounuil de Physique, voliiniL' 2 of 1V21. 

 They were taki'ii Uofori- tlii' lati-si iniprovuiiKMits were made in the apparatus, and 

 .|(. not <h<i» .,1. nine h r|,iail as the sketches; or perhaps the repro<Uirt ions are imperfcci . 



