( 440 ) 



A few experiments were tried to siihliine Diixtures of the two 

 coinpoiuHls. Tlie deposit on the coiu'iive ('overiiigf>li"ts.s then consists 

 of ji network of dent rit ic, sti-on,i>lv pleocliroïc (eolonrless — yellowish- 

 ,i>i'een) little ciTstals, (between which are found the s(pii\i'e-sliaped 

 crystals of the nitroso-componnd, besides the yellow indi\idiials of 

 the nitro-coinpound, united in (dusters. 



The first mentioned crystals contain chietiv the nili'oso-coni|)onnd 

 and })i-ol»al>ly to a very small amount also the nilro-com])Ound, so 

 this mav be a new case of the formation of solid solutions by 

 sublimation. Probably, this pair of compounds lends itself to the 

 measuring of the vapour tensions of these solid solutions. 



Zdaiuhiin, December J 907. 



Physics. — "Ohsi'fvat/on of ihc iikkjiicIIc resoliil'ion of spectral 

 lines hij iiicdiis of the melliod of Fabry and Pekot." By 

 Prof. P. Zkeman. 



The interference method of the parallel semi-silvered plates, worked 

 out with so much ingenuity by Fabry and Pkrot') excels above all 

 other spectroscopic modes of procedure by the accnracy with which 

 its theoretical foundations may be ])ractically realized. 



The principal task of the experimenter iji applying this method 

 has become to elfect the ))erfect parallelism of the reflecting sihercd 

 plates. 



In order to test by an iu(le|)endent method some recent results 

 obtained in an iu\ cstigation of tlie magnetic resolution of spectral 

 lines") the method of Fabry and Perot seemed most ajjpropriate. 

 Especially it appeared ])Ossible to extejid at the same time the in- 

 vestigation to the behaviour of the lines in Nveak fields. The present 

 pa[)er is pi'eliminary to a discussion of numerical results. 1 think it 

 beforehand \ ery im[)robable that errors of ruling of the Rowland 

 grating will turn out to be the reasoji of the asymmetrical I'esolution 

 of some lines, which I ha\e described. 



The method of Fabry and Perot is ai)j)lied in the present paper 

 for the tirst time to an investigation of the magnetic separation of 

 spectral lines. In some [)laces i]i the literature of the subject the 

 opinion is expressed that the method of interference fringes of 

 silvered lavers cannot be used for the subject under review. The 



^) Fabry el 1*erot, Ann. de Chimie cl de Physique lis99— 1904. 

 "j ZEf;.MA.N, These Proceedings, Noveniljei- 1907. 



