and  the  Magnetic  Relations  of  the  Heavenly  Bodies.       357 
Such  differences  may  very  well  be  caused  by  the  earth's  sur- 
face being  covered  with  or  bared  of  ice  and  water ;  and  in  this 
way  the  configuration  of  the  continents  may  have  a  certain  in- 
fluence on  the  earth's  magnetism*. 
9. 
The  facility  with  which  the  so-called  magnetic  disturbances 
and  their  connexion  with  volcanic  processes  are  explained  by  the 
aid  of  my  theory  is  of  much  greater  importance  than  all  the  facts 
given  above. 
In  fact,  every  sudden  change  in  the  velocity  of  the  streaming- 
masses  must  cause  in  them  a  wave-like  disturbance  and  an  ana- 
logous disturbance  in  the  position  of  the  magnetic  needle ;  it 
does  not  matter  whether  this  change  is  called  forth  by  the  break- 
ing away  and  falling  down  of  some  parts  of  the  earth's  crust  or 
by  a  volcanic  eruption,  or,  finally,  by  earthquakes  produced  by 
one  of  these  two  causes.  I  cite  again  some  passages  from  the 
above-mentioned  work  of  Lamont  which  refer  directly  to  the 
phenomena  we  are  now  discussing.  He  says,  speaking  of  the 
character  of  the  magnetic  disturbances  :  — 
"  If  a  great  disturbance  takes  place,  there  is  produced,  as  re- 
gards declination,  only  an  oscillation  about  the  mean  direction; 
the  mean  declination  of  the  disturbed  days  does  not  differ  from 
the  usual  means.  It  is  otherwise  with  the  remaining  mag- 
netic elements  :  every  large  disturbance  causes  a  decrease  in  the 
horizontal  intensity  and  an  increase  in  dip  ;  and  usually  several 
days  pass  before  the  mean  position  is  again  obtained.  Herewith 
the  often-noticed  fact  is  connected  that  a  disturbance  of  great 
amount  repeats  itself  the  following  days,  but  coming  always  at 
an  earlier  hour  than  before  and  with  decreasing  strength." 
Imagine  a  large  block  of  rock  torn  away  at  a  certain  hour  by 
the  glowing  streams  under  our  feet  and  disturbing  the  fluid 
mass  by  its  sudden  sinking  and  pendulum-  like  rising  and  falling. 
The  propagation  of  such  an  undulatory  movement  and  its 
periodical  return  with  decreasing  strength  might  perhaps  be  the 
cause  of  the  above  phenomenon. 
The  characteristic  properties  of  all  large  disturbances  men- 
tioned above  (viz.  the  decrease  of  horizontal  intensity  and  increase 
of  dip)  are  also,  I  believe,  easily  explained  by  my  views. 
Imagine  the  surface  of  a  globe  covered  with  insulated  wires 
parallel  to  the  circles  of  latitude.  Let  an  electrical  current  be 
sent  separately  through  every  turn  of  the  wire  in  the  same  direc- 
tion. This  globe  will  then  represent  the  earth  as  it  is  surrounded 
by  electrical  currents ;  and  a  magnetic  needle  fixed  on  the  surface 
*  Lenz,  "  Researches  on  an  irregular  distribution  of  the  Earth's  Mag- 
netism in  the  northern  part  of  the  Gulf  of  Finland,"  JSUm.  de  St.  Peters- 
bourg,  vol.  iii.  pp.  1-38. 
