( 471 ) 



to professor Aronstkin and i>rof<'ss(»r Sciiroedkr van DKR Koi.k for 

 their assistaiiec of vai-i<Mis kinds and to these I tender my best tlianks. 

 Also to Professor H. A. liOitKNTZ. professoi- at the Leyden University, 

 for his help and information. 

 M'uierahxiiail Jjdboratori/. 



Folyt. School Delft, Jan. 190:3. 



(February 25, 1903). 



