472     Prof.  W.  H.  Bragg  and  Mr.  R.  D.  Kleeman  on  th 
ie 
shows  that  the  first  deflexion  was  to  57*47  cm.,  and  then 
back  to  54*92,  zero  being  -4700.  The  experiment  repeated 
gave  57*42  to  54*92,  and  again  57*47  to  54*93.  The  leak 
was  also  measured  with  a  metal  plate  over  the  radium,  and 
the  difference  taken  as  the  proper  value  of  the  leak  for  that 
experiment,  a  small  proportion  only  being  due  to  /3  rays. 
The  first  measurements  relate  to  a  chamber  of  depth  6  turns — 
(i.)  under  a  potential  gradient  of  601)  volts  for  the  6  turns  ; 
(ii.)  a  gradient  of  20  volts  for  the  same  distance  ;  (iii.)  under 
600  volts  again.  The  difference  between  (i.)  and  (iii.),  as 
shown  in  the  table,  was  due  to  the  variation  in  sensitiveness 
of  the  electrometer.  In  almost  all  our  experiments  this 
variation  has  been  negligible  ;  in  this  special  case  it  was  not 
so,  because  so  large  an  amount  of  radium  was  used,  viz., 
5  mmg.  The  7  rays  penetrated  all  the  metal  casings,  and 
caused  a  leak  in  the  charge  of  the  needle.  The  leak  had  an 
exaggerated  influence  on  the  readings  because  the  capacity 
of  the  electrometer  was  increased  by  the  addition,  in  parallel, 
of  a  plate-condenser  of  1000  cm.  capacity.  This  disturbed 
the  usual  balance  of  the  electrometer,  in  which  leakage  of  the 
needle's  charge  had  little  effect  on  the  deflexion  for  a  given 
quantity  of  electricity.  To  obviate  any  error  from  variation 
of  sensibility  the  results  of  (i.)  and  (iii.)  were  averaged,  and 
compared  with  the  result  of  (ii.) .  It  will  be  observed  that 
successive  determinations  of  the  same  leak  were  very  con- 
sistent with  each  other.  This  implies  that  almost  all  the 
observed  effect  was  due  to  the  radium  ;  extraneous  influences 
were  very  small. 
G  Turns.     Zero  =  4700. 
GOO  volts         J  47 
(Metal  over  Ea).     47 
•I-  600  volts 
20  volts 
(Metal  over  Ea). 
20  volts. 
600  volts 
(Metal  over  Ea). 
600  volt.';. 
54 
47 
47 
55 
58 
li  Lq  J  Mean  leak 
63  59  J 
47  42  471  Ar 
92  92  93]Mean: 
07 
019  J 
Net  leak  =  852 —I6  (say). 
50  54] 
40  46  f 
Mean  =  48 
I 
i  49  39  491  .r  ^,0 
I  43  36  42     Mean  =  '4o, 
Net  leak  =  695  =  l\l 
47  i  70  691.r 
.„  :  P1    _.  y  Meai 
4<   ;  61  00  J 
1)4 
I 
57  i  19  16  13  1  ,r  CQo( 
54  i  73  70  66  )  Meaa  =  b93J 
Net  leak  =  829 
Value  of  I' 
695. 
