Am.  Jour.  Pharm. 
July,  19 1 9. 
Sir  William  Crookes. 
445 
his  powers  of  philosophical  deductions.  His  researches  covered 
various  fields  of  chemistry  and  physics,  but  chiefly  those  which  were 
within  the  borderland  of  these  two  branches  of  science.  His  name 
was  almost  equally  known,  by  his  long-continued  publication  and 
his  editorship  of  the  Chemical  News,  one  of  the  best  known  weekly 
chemical  journals,  and  the  authorship  of  a  number  of  chemical  and 
technical  manuals. 
He  was  one  of  that  class  of  students  who  obtained  their  earliest 
chemical  education  at  the  Royal  College  of  Chemistry,  then  under 
Professor  Hoffmann,  from  which  institution  it  will  be  remembered, 
came  the  brilliant  work  of  Perkin,  and  the  discovery  of  the  first  of 
the  aniline  dyes,  together  with  other  valuable  work,  about  the 
middle  of  the  last  century. 
Crookes,  for  a  short  time,  acted  as  an  assistant  to  Hoffmann  and 
became  a  lecturer  on  chemistry  in  Chester,  but  after  a  short  teaching 
experience  he  returned  to  London  and  founded  the  Chemical  News, 
which  he  edited  almost  to  the  end  of  his  long  life.  It  is  interesting 
to  note  that  among  the  earliest  matters  which  appeared  in  this 
journal,  were  Crookes'  reports  on  Faraday's  famous  Christmas  lec- 
tures at  the  Royal  Institution  on  "The  Chemical  History  of  the 
Candle." 
About  this  period  the  researches  of  Bunsen  and  Kirchoff  on 
spectrum  analysis,  leading  to  the  discovery  of  caesium  and  rubidium, 
were  made  known  to  the  scientific  world.  Crookes  immediately 
became  interested  in  the  use  of  this  new  method  of  analysis  and 
with  its  aid  made  his  first  important  contribution  to  chemical  sci- 
ence in  the  discovery  of  another  new  element — thallium.  His  re- 
searches upon  the  new  metal  led  him  into  the  study  of  other  mate- 
rials, with  the  aid  of  spectrum  analysis  and  he  made  an  extensive 
study  of  pure  selenium.  In  connection  with  the  very  careful  study 
of  these  relatively  rare  metals,  Crookes  was  led  to  make  his  weigh- 
ings on  a  delicate  balance  in  vacuo.  When  these  weighings  were 
made  in  this  way  and  in  full  daylight,  irregularities  in  the  action 
of  the  balance  became  evident  to  the  keen  observer.  He  thus  found 
that  light  objects  which  were  free  to  move  in^high  vacua  could  be 
made  to  do  so  by  mere  exposure  to  light,  and  the  result  was  the 
discovery  of  the  now  familiar  "  Crookes'  radiometer,"  the  vanes  in 
which  are  set  in  rapid  motion  when  a  beam  of  sunlight  is  allowed  to 
fall  on  the  apparatus.    This  study  of  such  "  repulsion  resulting 
