362     M.  P.  Zollner  on  the  Origin  of  the  Earth's  Magnetism, 
Lamont,  indeed,  draws  our  attention  to  the  fact  that  the 
causes  which  generate  a  daily  period  in  the  changes  of  the  mag- 
netic constants  are  as  a  rule  only  increased  by  the  disturbances, 
so  that  the  latter  may  be  considered  to  be  only  reinforcements 
of  the  causes  which  generate  the  daily  variations.  The  words  of 
Lamont  upon  this  subject  are  (in  the  work  mentioned,  p.  271) 
the  following : — 
"  Every  hour  in  the  day  has  its  own  predominant  disturbances  ; 
and  in  general  they  are  only  reinforcements  of  the  daily  varia- 
tions. We  find,  for  instance,  that  if  the  declination  is  in  its 
westward  motion,  it  sustains  by  the  disturbing  force  an  impulse 
towards  the  west,  and  if  it  is  moving  eastward  it  receives  an  im- 
pulse towards  the  east." 
The  following  remarks  of  Lamont  seem  to  me  to  be  equally 
correspondent  to  the  above  consequences  of  my  theory,  if  we 
remember  the  influence  of  the  time  of  the  day : — 
"  If  we  compare  the  simultaneous  observations  made  in  Peters- 
burg, Katherinenburg,  Barnaul,  Nertschinsk,  Sitka,  Makerstoun, 
which  are  all  near  the  parallel  of  55°,  we  find  that  when- 
ever a  large  disturbance  takes  place  in  Petersburg,  as  often 
happens,  the  needle  in  Katherinenburg  turns  towards  the  same 
direction  but  describes  a  much  smaller  path ;  in  Barnaul  and 
Nertschinsk  the  movement  is  in  the  same  sense  but  almost  va- 
nishes. Most  likely  further  to  the  east  it  disappears  entirely, 
and  reappears  in  Sitka  in  the  opposite  sense.  In  Makerstoun 
the  disturbance  takes  place  in  the  original  form,  but  less  intense 
than  in  Petersburg. 
ts  Almost  all  the  more  important  disturbances  manifest  them- 
selves in  the  manner  described ;  and  I  think  it  highly  probable 
that  there  do  not  exist  more  than  one  source,  but  that  all  the 
disturbances  have  the  same  origin  and  the  same  course ;  they 
are,  however,  as  already  stated,  modified  by  the  time  of  day." 
In  a  still  more  characteristic  way  the  agreement  of  the  nature 
of  the  disturbances,  as  deduced  from  my  theory,  for  places  in  the 
same  latitude,  is  shown  by  the  following  words  of  Miiller* : — 
"For  different  places  having  nearly  the  same  latitude  but  dif- 
ferent longitudes,  a  connexion  between  the  disturbances  is  found 
but  in  a  different  manner.  If  at  any  time  a  particularly  strong 
disturbance  take  place  at  a  certain  spot,  it  will  appear  towards 
east  and  west  in  the  same  direction  but  with  decreasing  strength; 
at  90°  to  the  east  and  90°  to  the  west  from  the  place  where  the 
disturbance  has  its  maximum  at  the  same  moment  only  very 
weak  oscillations,  if  any,  will  be  observed ;  on  the  other  half  of 
the  parallel  the  simultaneous  deflections  have  another  direction, 
*  Kosmische  Physik,  third  edition,  1872,  p.  761. 
