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XXXI. The Effect of Electric and Magnetic Fields on the 

 Emission Lines of Solids. By C. E. Mendenhall and 

 K, W. Wood*. 



[Plate IV.] 



SO little is yet known about the cause and real nature 

 of the Stark-Lo Surdo effect, that a search for it under 

 any experimental conditions different from those used by its 

 discoverers is certainly worth while. This is the more true 

 since Paschen f failed to detect any electric decomposition 

 of the Hg 2536*7 line excited by resonance according to the 

 method used by one of the present writers %. It is true 

 Paschen's method was indirect, but it should be extremely 

 sensitive as* a qualitative test. Pascheir's negative result 

 raises the question which started the present work, namely, 

 is the absence of any influence of an external electric field 

 due in this case to the nature of the vibrating system giving 

 this line, as compared with the system giving other mercury 

 lines for which the effect has been demonstrated §, or is it 

 due to the different method of excitation ? For, with this 

 exception, all sources so far examined for the Stark effect 

 have been excited by canal -ray bombardment, and it seemed 

 possible that this mode of excitation might be a necessary, 

 though not a sufficient, condition for obtaining the effect. 



It was therefore proposed to look for the Stark effect in 

 solids, both with fluorescent emission lines and with absorp- 

 tion lines, in the hope of finding an " inverse " effect. 

 Incidentally, some other aspects of these fluorescent and 

 absorption lines were examined, and the results are included. 



It should be said at once that, as regards the Stark effect, 

 the results have all been negative ; but it seems to us that 

 negative results in this connexion are of sufficient interest 

 to warrant a description of the conditions under which they 

 were obtained. 



Apparatus. — Two plane grating spectrographs were used 

 from time to time, one of 1 metre focus using about 4 inches of 

 ruled surface, 15,000 lines per inch, the other 3 m. focus and 

 6 in. ruled surface, in each case in the 1st order spectrum. 

 The definition and light efficiency of these instruments were 

 excellent ; without exposing for more than an hour the slit 

 could be used in every case so narrow that resolution was 

 limited by the physical width of the lines. All but a few 



* Communicated by the Authors. 



t Paschen & Gerlach, Phys. Zeit. May loth, 191 4. 



X Wood, Phil. Mag. April, 1913, p. 433. 



§ Wendt & Wetzel, Phys. Eev., Nov. 1914, p. 549 (abstr.). 



