450     M.  F.  Zollner  on  the  Origin  of  the  Earth's  Magnetism, 
Let  us  recall  to  our  minds  the  kind  of  effects  which  could  be 
produced  in  the  earth  by  such  an  induction.  They  are  two- 
fold, viz. : — 
1.  Mechanical  effects,  by  changes  in  the  velocity  of  the  glow- 
ing streams  in  the  earth. 
2.  Magnetical  or  electrical  effects,  necessarily  connected  by  our 
theory  with  these  mechanical  changes. 
As  to  the  first  of  these  two  influences,  it  is  clear  that,  if  the 
origin  of  terrestrial  magnetism  is  really  to  be  sought  in  the  glow- 
ing streams  and  the  electrical  currents  necessarily  produced  by 
them,  any  increase  or  decrease  in  the  magnetism  by  induction 
must  produce  an  increase  or  decrease  in  the  velocity  of  these 
glowing  streams. 
It  has  already  been  shown  above  how  the  magnitude  of  the 
disturbing  influences  must  vary  with  the  magnitude  of  velocity 
of  these  streams,  and  how,  therefore,  at  the  time  of  the  greatest 
magnetic  induction  a  maximum  of  earthquakes,  of  magnetic  dis- 
turbances, and  of  aurora?  boreales  must  take  place,  which  latter 
are  produced  by  electrical  induction  in  the  rarefied  regions  of 
our  atmosphere. 
Theoretically,  changes  in  the  temperature  of  the  earth  must 
accompany  these  phenomena  which  manifest  themselves  on  the 
earth's  surface.  For,  as  we  have  already  remarked  (p.  349), 
the  increase  or  decrease  in  the  vis  viva  of  the  streams  can,  ac- 
cording to  the  principles  of  the  conservation  of  energy,  only 
take  place  if  an  equivalent  amount  of  vis  viva  disappears  in  an- 
other part  of  the  system.  Any  large  and  not  wholly  solidified 
heavenly  body  presents  us,  besides  its  translatory  and  rotatory 
motion,  its  store  of  energy  in  two  forms  : — 
1.  In  the  form  of  heat,  which  is  continually  diminishing  by 
radiation. 
2.  In  the  form  of  mechanical  motion  in  the  currents  of  its 
liquid  and  gaseous  constituents. 
If  one  of  these  two  forms  of  energy  is  increased  or  diminished 
without  exterior  communication  of  vis  viva,  it  must  be  at  the  ex- 
pense of  the  other. 
If,  therefore,  by  magnetical  induction  the  velocity  of  motion  is 
increased,  it  must  be  accompanied  by  a  decrease  of  temperature, 
and  vice  versa. 
Suppose  therefore  a  physical  cause  to  exist  by  which  the  mag- 
netic condition  of  the  sun  is  periodically  changed.  According  to 
what  has  been  said,  a  variation  in  the  earth's  temperature  must 
be  produced  by  the  simultaneous  variations  in  the  magnetic  in- 
duction of  the  earth.  This  change  of  temperature  will  be  the 
more  perceptible  the  deeper  the  thermometer  is  let  down  into  the 
earth,  and  the  nearer  therefore  it  is  to  the  glowing  liquid  interior. 
