632      Messrs.  Hawthorne  and  Morton  on  Deflexions  caused 
2  he  Positive  Charge  of  the  a  Particle. 
Considerable  discussion  has  recently  taken  place  as  to  the 
mode  in  which  the  a.  particle  acquires  its  positive  charge.  It 
has  been  pointed  out  more  that  once  that  it  may  be  explained 
as  the  result  o£  ionization  by  collision  (Rutherford,  Address 
to  Congress  at  St.  Louis,  1904 ;  Bragg,  Phil.  Mag.  Dec.  1904), 
and  that  the  same  hypothesis  will  explain  the  deposit  of  the 
radium  emanation  on  the  negative  electrode  (Bragg  and 
Kleeman,  Phil.  Mag.  Dec.  1904) .  In  the  case  of  the  emanation 
an  explanation,  which  I  understand  to  be  similar,  has  been 
carefully  worked  out  by  Makower  (Phil.  Mag.  Nov.  1905). 
Rutherford  has  shown  that  the  a  particle  is  charged  at  the 
moment  of  leaving  the  radium  salt.  But  I  do  not  think  that 
the  result  is  in  any  way  prejudicial  to  the  collision  theory. 
He  evaporated  a  very  weak  solution  of  radium  on  a  plate, 
and  supposed  that  as  a  result  he  had  an  excessively  thin  layer, 
so  that  the  particle  made  very  few  collisions  before  emergence. 
But  when  such  deposits  are  examined  under  a  microscope,  it 
is  seen  that  the  salt  is  gathered  in  little  heaps,  and  there  is 
no  true  layer  at  all.  The  bulk  of  the  a.  particles  pass  through 
hundreds  of  atoms  before  emergence,  and  there  is  ample 
opportunity  for  ionization  by  collision. 
We  find  that  the  a  particle  spends  energy  in  causing  the 
expulsion  of  electrons  from  the  atoms  of  any  gas  which  it 
traverses.  We  find  also  (see  Tables  A  and  B,  above)  that 
the  expenditure  of  energy  by  the  a  particle  follows  the  same 
law  when  the  atoms  are  massed  together  in  a  solid.  The 
solid  must  therefore  be  ionized,  just  as  the  gas  is,  and  we 
should  expect  slow-moving  electrons  to  be  projected  from  Ra 
itself,  and  from  both  sides  of  any  solid  screen  through  which 
the  particles  pass.  Surely  this  is  the  effect  lately  observed 
by  J.  J.  Thomson,  Rutherford,  and  others.  This  has  been 
suggested  by  Soddy  ('Nature/  March  1905). 
LYII.  Kote  on  the  Deflexions  caused  by  a  Break  in  an  Over- 
head Wire  carried  on  Poles.  By  W '.  Hawthok^e,  B.A., 
B.B.,  and  W.  B.  Morton,  M.A.* 
IN"  the  modern  conditions  of  electrical  power-transmission 
along  overhead  wires,  it  is  a  matter  of  practical  import- 
ance to  know  what  will  happen  in  case  a  wire  breaks.  The 
relaxing  of  tension  at  one  point  will  throw  a  one-sided  pull 
on  the  range  of  poles  on  either  side  of  the  break;  and  it  is 
essential  for  safety  that  the  maximum  deflexion  thus  produced 
should  be  below  a  definite  limit. 
*  Communicated  by  the  Authors. 
