mentary  current  is  produced  in  the  same  direc-
tion. This  produces  attraction.
Now,  regarding  the  same  phenomena  from  the
standpoint  of  lines  of  magnetic  force,  when  a
conductor  through  which  a  current  is  passing  is
placed  in  a  magnetic  field,  any  increase  in  the
number  of  lines  of  magnetic  force  passing  through
it  tends  to  move  the  conductor  out  of  the  magnetic
field,  while  any  decrease  in  the  number  of  lines
of  force  tends  to  move  the  conductor  into  the
field.  To  experimentally  show  the  attractions
and  repulsions  produced  by  magnetization  or
demagnetization,  the  following  apparatus  may  be
employed :

A  stout  disc  of  copper,  Fig.  200,  is  supported
on  a  horizontal  arm  in  the  position  shown  in  front
of  the  pole  of  a  powerful  electro- magnet.  When
the  current  is  sent  through  the  electro-magnet  the
disc  of  copper  is  repelled  from  the  magnetic  pole.
When  the  magnetism  is  being  destroyed  by  the
opening  of  the  circuit  and  by  the  weakening  of
the  current,  the  copper  disc  is  attracted.
Diamagnetometer. — An  apparatus  de-
signed for  studying  diamagnetism.  (See  Dza-
magnetism.}

The  apparatus  for  the  study  of  paramagnetism
generally  receives  simply  the  name  of  magnet-
ometer.
Diamagnets.  —  Diamagnetic  substances
subjected  to  magnetic  induction  and  formerly
called  diamagnets  in  contradistinction  to  or-
dinary magnets.
Diamagnets  are  supposed  by  some  to  possess  a
polarity  the  same  as  that  of  the  inducing  pole,
instead  of  the  opposite  polarity,  as  in  paramagnetic
substances.  (See  Diamagnetism.')

Diaphragm. — A  sheet  of  some  solid  sub-
stance, generally  elastic  in  character  and  cir-
cular in  shape,  securely  fixed  at  its  edges  and
capable  of  being  set  into  vibration.
