320 On the Emission Lines of Solids, 



showing no corresponding absorption, no synchronous reson- 

 ance, no Zeeman and no Stark effects ; this line may not be 

 a normal mode ; the other shows absorption, resonance, 

 radiation, and Zeeman effect, but no Stark effect, and 

 apparently is a normal mode. 



From among the substances known * to have fine visible 

 absorption lines the following were selected for experiment : 

 monazite, praseodymium sulphate, neodymium sulphate, 

 neodymium nitrate, uranyl nitrate. Taking these in order., 

 monazite absorption lines were examined visually only, in 

 liquid air, the narrowest line being then about 6 A. IT. wide. 

 A field of 45,000 volts/cm. produced no change. Praseody- 

 mium sulphate in liquid air gives a very beautiful group of 

 absorption lines about 5900 A.U., the narrowest and sharpest 

 being less than 1 A.U. wide. A field of 60,000 volts/cm. 

 gave no shift or change in appearance. Neodymium sulphate 

 in liquid air gives a number of beautifully fine lines ; 

 examined both visually and photographically with 60,000 

 volts/cm. ; no effect. Neodymium nitrate in liquid air,, 

 examined visually and photographically, for both the longitu- 

 dinal and transverse effect with lines in the blue and red 

 regions, same field as above ; no effect. Uranyl nitrate under 

 the same conditions showed no effect, though the lines are- 

 not as sharp as those of the neodymium salts. 



It may be urged with reference to all of these negative 

 results, that they are simply due to the neutralization of the 

 external field by the internal field developed by the strain of 

 the atomic structure, as Stark f suggests in the case of gases, 

 or of the crystalline arrangement. There is no reason,, 

 however, to expect such neutralization to occur in general. 

 It might, however, be worth while to test this point by 

 submitting solids to an alterating electric field of high fre- 

 quency, say from a Tesla coil, which frequencies, since they 

 are high enough to greatly alter the measured dielectric- 

 constants, would probably be high enough to prevent complete 

 neutralization. A further search for a possible Stark effect 

 with vapour fluorescence seems also to be very much worth 

 while, and we have such an examination under way with 

 iodine vapour. It would also be worth while to search for 

 the Stark effect with canal-ray and fluorescent excitation 

 applied to the same line of the same substance, which has 

 not been possible with the materials we used. 



Physical Laboratory of Johns Hopkins University. 



* From the work of J. Becquerel, Le Radium, v. p. 5 (1908), and 

 Du Bois & Elias, Ann. d. Phys. xxxv. p. 617 (1911). 



t Stark, Elektrische Spehtralanalyse Chemischer Atome, Leipzig, 1914,. 

 p. 127. 



