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Views  on  Constitution  of  the  Atom.  -jA 
produced  by  the  particle,  particularly  the  negative  ions,  are  urged 
forward  with  a  very  high  velocity  by  the  intense  electric  field,  and 
these  ions  produce  more  ions  by  collision.  It  is  as  though  a  temporary  v 
minute  spark  passed,  so  that  the  needle  leaps  up  from  zero  to  36  or  40 
volts.  As  the  needle  is  connected  to  the  quartz  fibre  FF  this  latter  is 
at  once  charged,  and,  being  between  charged  plates,  is  deflected.  A 
stable  state  is  swiftly  re-established,  owing  to  the  high  resistance  R, 
and  the  trap  is  reset  to  show  the  next  electron.    The  movements  of 
Fig.  2. — B  is  a  hollow  brass  cylinder  (4x1  cm.)  with  a  small  hole  in  the  end  (where  the 
electron  enters),  Voltage  +  1500.  N  is  a  fine,  sharp,  clean  needle  with  its  point  about  8  mm. 
from  the  hole.  R  is  a  high  resistance,  about  100  megohms,  of  xylol  and  alcohol  in  a  glass  U 
tube.  FF  is  a  fine,  silvered,  quartz  fibre  between  two  metal  plates  8  mm.  apart,  15  cm.  long, 
charged  to  low  opposite  voltages. 
the  quartz  fibre  are  seen  when  projected  on  a  white  screen.  With 
this  apparatus  many  beautiful  experiments  can  be  shown,  such  as  the 
range  of  the  alpha  particles  from  polonium ;  individual  alpha  particles 
passing  through  a  pinhole  in  paper;  the  reflection  of  scattering  of 
rays  from  lead  or  from  aluminum,  in  which  case  the  lead  is  the  more 
effective;  the  long-distance  effect  of  the  gamma  rays  and  their 
highly-penetrating  nature.  But  the  most  excellent  and  impressive 
sight  is  that  of  a  piece  of  pitchblende,  just  as  it  came  from  the  mine 
in  Bohemia,  continually  expelling  alpha  and  beta  particles  into  the 
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