the  a,  Rays  from  Radiotliorium. 
805 
screen.     If  the  value  of—    is  the  same  for  the  a  particles  of 
m 
thorium    and   radium,  that  suggests  that  the  a  particles   of 
range  8*6   cms.  are  expelled  with  a  greater  speed  than  those 
from  radium  C.     Such  a  result  is  in  agreement  with  the 
greater  range  in  air,  8'6  cms.,  of  the  rays  from  the  thorium 
product,  for  the  rays   from  radium  C  have  a  range  of   only 
7*0  cms. 
Further  experiments  are  in  progress  with  Prof.  Rutherford 
6 
to  determine  accurately  the  velocity  and  value  of  —  for  the 
j  j  m 
a  particles  expelled  from  the  active  deposit.  The  experiments 
are  difficult  on  account  of  the  weak  photographic  effects  of 
the  sources  employed. 
It  may  not  be  without  interest  to  give  here  a  table  of  the 
thorium  products,  so  far  as  they  are  yet  known. 
Products. 
Nature  of  rays 
emitted. 
Time  for  product 
to  be  halt* 
transformed. 
Thorium. 
1 
Eadiothorium. 
1 
Thorium  X. 
1  . 
Emanation. 
1 
Thorium  A. 
1 
Thorium  B. 
I 
Thorium  C. 
1 
? 
probably  rayless. 
a  rays. 
a     „ 
a     ,, 
rayless. 
a  rays. 
«5  &  7    » 
about  109  years. 
? 
4  days. 
54  seconds. 
10-6  hours. 
1  hour. 
a  few  seconds  ? 
In  conclusion  I  express  with  much  pleasure  my  gratitude 
to  Prof.  Rutherford  for  his  permission  to  work  in  the 
McGrill  Physics  Building  and  for  the  kindness  and  assistance 
which  he  so  readily  gives  on  all  occasions. 
McGill  University,  Montreal, 
