( 740 ) 



The sufficiently good agreement of the ratios proves the pro- 

 portionality of the resolution with the intensity of the tield, at least 

 as a first approximation ; it is rather improbable that weaker fields 

 should exhibit any deviations from this proportionality. 



§ 18. Almost analogously behave the lines iji the 



2. Extraordinarij ,spectimm\ i)lane of polarisation vertical. 



A. Pair of bands in the hlue at —193°. The width with field off 

 amounted to 0,10 for B^, to 0,15 ^i,« for 5.,, the distance of the middle 

 lines was 1,70 fxft; the lines appear somewhat displaced compared 

 with the ordinary spectrum, viz. B^ 0,025 im towards red, and B^ 

 0,007 towards violet; moreover B^ was vaguei- and paler than />',. 



In a field of 36 kgs. the widths became 0,18 and 0,22 fiu ; so for 

 B^ and B^ respectively half the increase in width amounted to 0,04. 



B. Pair of bands in the ird at —193°. The width with tield oif 

 amounted to 0,07 for R^, to 0,06 mi foi- t{.„ their distance being IMm- 



They both seem to have shifted 0,02 /x/t towards the violet, com- 

 pared with their position in the ordinary spectrum ; R^ is fainter. 



With 36 kgs. R^ exhibits a quadruplet of 4 lines about equally 

 strong, at apparently equal distances, too indistinct, however, to be 

 measured; distance of the extreme limits 0,49 fi/i; the middle appeared 

 to have moved 0,02 ft/t towards the violet with respect to the position 

 with tield off. 



For R^ the iuner lines of the 4 were i)robably slightly stronger 

 than the outer ones ; the determinations were rather uncertain ; the 

 distance of the limits about 0,4 mi. 



§ 19. Fifth series. Of this we now investigated a few sul- 

 phates of the material used iu 1899, which crystallise monoclinically 

 as octohydrates ; they do so in plates containing both optical axes. 

 As a matter of course no circular polarisation occurs ; in this 

 respect uniaxial and even more so cubic crystals, e. g. chromium 

 alum, are to be preferred. 



Neodi/mium sulphate [Nd., (S0J3. 8 H,()]. Rosy-red plate 0,8 mm. 

 thick at — 193'. Two narrow bands in the yellow, and ihree in 

 the green exhibited au increase in width of from 0,05 to 0,08 (i[i 

 in a field of 40 kgs ; two of the last mentioned became brighter in 

 the middle, and so began to look like doublets. 



Samarium sulphate [Sm., (SoJ^ . 8 H.,0]. Light yellow semi-trans- 

 parent plate of crystal, 2,8 mm thick at —193°. Two narrow 

 bands iu the yellow-green exhibited an increase in width in a tield 

 of 28 kgs. the amount of which ought to be determined with a sample 

 of better transparency, 



