( 839 ) 



Physics. — "The influence of temperature and magnetisation on 

 selective absorption spectra." III. By Prof. H. E. J. G. du Bois 

 and G. J. Elias. (Communication from the Bosscha-Laboratorj). 



§ 20. Since our former communication (These Proc. March p. 734) 

 we iiave obtained a number of samples, the crystallisation of which 

 in reasonable sizes from solutions in water or amylic acetate was 

 brought about only after many failures and many weeks of patience. 

 Notices concerning the influence of the anion or the temperature only 

 on the absorption spectrum, must be laid aside as being too extensive, 

 though incidentally some details may appear about it. With respect 

 to the ZEEMAN-efFect we shall also confine ourselves to a choice from 

 the profuse material, which for the present can be little more than 

 an enumeration of the many ways in which the influence of the 

 magnetisation may manifest itself; it must be reserved for further 

 investigation to impart more order and regularity to the present 

 rather unsystematic series of results. 



As a rule we worked again in the spectrum of the first order ; in 

 some cases we had recourse to the second order, in which some 

 special effect may sometimes be better judged, at least from a 

 qualitative point of view; for measurements the first order proved 

 preferable on the whole. As we have never to do with very fine 

 lines, too great a dispersion is of no use here, and certainlv of 

 much less importance than a strong magnetic resolving power. Very 

 thin crystal chips — some tenths of a mm. thick — alreadj^ exhi- 

 biting jet-black absorption bands, particularly for neodymium salts, 

 we could use these, and expose them to very strong fields, mostly 

 of 38 — 42 kilogauss. The distinctness of the spectral image depends 

 to some extent on the choice of the proper thickness for every salt. 

 The fields were measured with a bismuth spiral; the disturbance by 

 the narrow slits is certainlj^ less than with the usual round bores; 

 the increase of the — saturated — magnetisation values of the polar 

 end-pieces on cooling them down to - 190^ is probably slight; it 

 would be desirable to obtain further information concerning these 

 points. We consider, however, the accuracy of our field-measurements 

 of the same order as that of the readings in the spectrum. We again 

 preferred the latter to a photographic reproduction; for with visual 

 observation the identification of the lines with field on and field off, 

 especially with erbium compounds, proved to be decidedly easier. 



^ 21. Third series. We have investigated a few organic 

 double salts of chromium and potassium with a view to a possible 



