830 
Experiment  with  the  Electric  Arc. 
So  long  as  the  aluminium  diaphragm  "  D "  remained 
intact,  the  electrometer  showed  that  no  appreciable  electrical 
charge  was  imparted  to  the  Faraday  cylinder,  whether  "  A  *' 
was  made  positive  and  "B  "  negative,   or    vice  versa;  the 
Ktf  1. 
aluminium  diaphragm  being  apparently  quite  impervious  to 
any  electrical  carriers  that  obtained  access  to  the  interior  of 
the  pierced  electrode.  On  several  occasions,  however,  in 
vacua  of  about  750  mm.  of  mercury,  when  "  B  "  was  positive 
and  "A  "  negative,  after  the  arc  had  been  in  existence  for  a 
few  seconds,  a  sudden  and  permanent  deflexion  of  the 
electrometer  showed  that  something  had  occurred  that  had 
allowed  a  positive  charge  amounting  to  several  volts  to  reach 
the  Faraday  cylinder  ;  and  once  this  condition  had  been 
arrived  at,  on  reversing  the  current  and  making  "  B  " 
negative,  the  electrometer  showed  a  similar  negative  charge. 
On  removing  the  aluminium  diaphragm  after  each  of  these 
occasions,  it  was  found  to  be  perforated  by  several  very 
minute  holes  which  were  just  visible  to  the  naked  eye  on 
holding  up  the  diaphragm  to  a  strong  light,  and,  on  being 
examined  with  a  microscope  of  moderate  power,  gave  un- 
mistakable evidence,  from  their  sharp  jagged  edges,  of 
having  been  caused,  not  by  fusion,  but  by  bombardment  by 
very  minute  particles  of  matter,  presumably  of  carbon,  shot 
