476  Intelligence  and  Miscellaneous  Articles. 
taining  227  grms.,  yet,  if  it  act  in  opposition  to  A.  it  can  diminish  the 
weight  which  the  latter  supports  by  327  grms.*;  that  is,  its  power  to 
demagnetize  is  greater  than  its  power  to  magnetize. 
If,  then,  we  suppose  the  coercive  force  of  the  steel  bar  used  in 
Wiedemann's  experiments  to  be  represented  by  the  helix  A,  and  the 
demagnetizing  current  of  feeble  intensity  to  be  represented  by  the 
helix  B,  of  less  magnetizing  power,  we  have  here  an  interesting 
confirmation  of  Wiedemann's  results;  while  we  may  also  extend 
the  application  of  the  principle  to  electromagnets,  and  may  assert, 
in  general,  that  a  current  of  given  intensity,  or  a  helix  of  given 
dimensions  traversed  by  a  constant  current,  has  greater  power  to 
demagnetize  trfan  to  magnetize.  It  is  evident  that  the  case  of  de- 
magnetizing an  electromagnet  by  a  current  is  more  difficult  than 
the  process  of  demagnetizing  a  steel  bar ;  for  whereas  in  a  steel 
magnet  the  resistance  is  simply  the  coercive  force  of  the  steel,  so 
that  the  bar  when  partially  deprived  of  its  magnetism  has  no  ten- 
dency to  return  to  its  original  state,  even  if  the  demagnetizing  cur- 
rent be  broken,  in  the  case  of  electromagnets  the  helix,  by  which 
the  bar  was  originally  magnetized,  is  still  acting  with  its  full  power 
when  the  demagnetizing  helix  is  introduced  into  the  circuit. 
A  natural  inquiry  was  this :  if  the  bar  were  magnetized  by  the 
weaker  helix  B,  and  then  demagnetized  by  the  helix  A,  what  addi- 
tional amount  of  magnetism  could  A  impart  to  the  bar  ?  It  is  evi- 
dent that  this  case,  though  somewhat  similar  to  the  former,  is  not 
identical  with  it ;  here  the  helix  B  acts  as  resistance  to  the  magnet- 
ization of  the  bar,  while  in  the  former  case  it  acted  to  deprive  the 
bar  of  a  portion  of  the  magnetism  which  it  already  possessed. 
Accordingly  the  bar  being  magnetized  by  B,  was  submitted  to  the 
action  of  A,  and  the  weight  supported  being  noted,  the  reverse  opera- 
tion was  performed,  and  the  weights  supportedcomparedas  follows  :  — 
A  demagnetized  by  B.  B  demagnetized  by  A. 
85  65 
70  65 
65  60 
65  50 
It  will  be  noticed  that  the  results  in  the  left  hand  are  larger  than 
those  in  the  right-hand  column  ;  that  is,  when  A  is  simply  demag- 
netized by  B,  it  can  support  a  greater  weight  than  when  it  is  em- 
ployed to  magnetize  the  bar  against  the  resistance  of  B. 
In  short,  the  result  of  my  experiments  has  been  to  show  that  a 
given  helix,  traversed  by  a  given  current,  has  more  power  to  demag- 
netize than  to  magnetize,  while  its  power  to  prevent  magnetization 
is  greater  than  either. — Silliman's  American  Journal  for  May  1872. 
THE  SOURCE  OF  THE  SOLAR  HEAT.       BY  MAXWELL  HALL,  B.A. 
Let  us  suppose  that  the  mass  of  the  sun  is  slowly  but  continually 
contracting ;  then,  in  consequence  of  the  enormous  mass  subjected 
to  this  contraction,  an  enormous  amount  of  heat  will  be  developed, 
and  it  will  be  found  that  the  rate  or  amount  of  contraction  neces- 
