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aid of what had been published bj him, but it tests them by a 

 number of compounds hitherto unknown; on the other side some 

 new points of view have come to light. Among these we may 

 mention tiie influence of the bifui-calion of the carbon chains, the 

 further differentiation of the atomic refi-action of oxygen, the influ- 

 ence of stereo-isomery, and the closer inquiry into the dispersion of 

 the organic compounds. 



This entire posthumous work shows with great evidence that there 

 can be no question of constant atom refractions, not even for carbon. 

 Though the variations in the atom refractions of this element are 

 often pretty insignificant, it yet does not constitute an exception to 

 the general rule that the atom refractions are not constant. 



Eykman's work aims at no less than a total revision oftherefrac- 

 tometry of organic compounds; he has treated in a masterly way 

 all the fundamental questions in this region, thanks to his great 

 gifts of research and his amazing energy, which have fortunately 

 remained unaffected under the depressing feeling of neglected merit. 



Amsterdam, January 1919. 



