PEOFESSOE  PLtiCKEE  ON  THE  MAGNETIC  INDUCTION  OF  CETSTALS.  577 
provided  a small  but  most  homogeneous  and  transparent  sphere,  on  whose  varnished 
surface  the  symmetrical  plane  was  marked  by  a great  circle. 
We  succeeded  first  in  establishing  the  former  observation.  The  sphere  of  sulphate  of 
iron  was  suspended  between  the  two  poles,  as  formerly  the  sphere  of  formiate  of  copper 
was,  with  this  difierence  only,  that,  on  account  of  the  stronger  paramagnetic  induction, 
we  made  use  of  only  two  of  Geove’s  elements  instead  of  six.  The  sphere  was  first 
placed  on  the  ring  with  the  symmetrical  plane  horizontal,  and  the  direction  within  it 
pointing  axially,  marked  by  a point  on  the  corresponding  great  circle.  The  sphere 
being  then  placed  on  the  ring,  with  the  symmetrical  plane  vertical  and  the  marked 
point  situated  in  the  vertical  axis  of  suspension,  did  not  move  under  the  influence 
of  the  magnetic  poles.  Hence  sulphate  of  hon  is  a uniaxal  positive  and  paramagnetic 
crystal. 
The  sphere  was  then  put  on  the  ring  successively  -with  its  symmetrical  plane  hori- 
zontal, and  inchned  45°  alternately  on  one  side  and  the  other. 
Hence 
The  symmetrical  plane.  Number  of  seconds  required 
for  twenty  oscillations. 
Inclined  -|-45°  .... 
Horizontal 
. 60 
44 
Inchned  —45°  .... 
Horizontal 
. . 64 
45 
Inclined  +45°  .... 
Horizontal 
. . 61 
46 
Inchned  — 45°  .... 
Horizontal 
. . 651 
45 
Inclined  +45°  .... 
Mean  numbers 
. . 631 
. . 62-8=00 
© 
II 
|«=0-715  sin  •vl/^sin  45°=0-707 ; 
therefore,  in  this  case  also,  the  theory  is  fully  confirmed  by  experiment. 
69.  Bemg  desirous  of  examining  in  like  manner  a uniaxal  and  diamagnetic  crystal, 
I selected  a beautiful  specimen  of  crystaUized  bismuth,  showing  the  cleavage  in  the 
most  perfect  way.  A sphere,  0°79  of  an  inch  in  diameter,  was  turned  out  of  it,  and 
on  its  surface  was  traced  the  equatorial  circle,  indicating  the  cleavage  plane,  and  any 
meridional  circle  passing  through  the  magnetic  axis.  But  this  sphere,  on  account  of 
the  electric  currents  excited  within  it,  while  it  oscillates  between  the  two  poles,  could 
not  be  subjected  to  experiment  in  the  same  way  as  the  sphere  of  sulphate  of  iron. 
'L'his  is  the  case  with  regard  to  all  substances  enjoying  a great  conducting  power,  and  not 
being  magnetically  influenced  in  so  high  a degree  as  iron,  cobalt,  and  nickel. 
79.  Therefore,  in  order  to  verify  the  theory  which  has  been  expounded  with  regard  to 
our  sphere  of  ciystallized  bismuth,  when  suspended  along  its  different  diameters,  we 
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