500     M.  F.  Zollner  on  the  Origin  of  the  Earth9 s  Magnetism, 
varying  from  600  to  36,000  metres,  and  a  difference  in  depth  of 
83  to  642  metres.  They  always  gave  concordant  results ;  but  the 
longer  wire  and  larger  difference  in  height  gave  a  stronger  current. 
As  regards  the  quality  of  these  currents,  Matteucci  discusses 
expressly  the  question  whether  they  are  to  be  regarded  as  branch 
currents.  He  answers  the  question  in  the  negative,  as  the  con- 
ductivity of  the  earth  must  be  assumed  to  be  infinitely  great 
in  comparison  with  that  of  the  wires. 
According  to  my  opinion,  nothing  else  remains  than  to  con- 
sider the  layer  of  earth  between  the  zinc  plates  electrically  active, 
similarly  to  a  voltaic  pile.  The  fact  that  the  intensity  of  the  ob- 
served currents  increased  with  the  interposed  layer  of  earth  would 
be  in  harmony  with  this  assumption. 
The  direction  of  the  current  within  the  earth  would,of  course, 
be  the  opposite  of  that  in  the  wires,  so  that  the  surface  of  the 
earth  would  be  surrounded  by  currents  flowing  from  east  to  west 
and  from  north  to  south. 
With  regard  to  the  diaphragmic  currents  of  Quincke,  it  would 
be  interesting  to  see  whether  the  moisture  constantly  descending 
in  the  earth  under  great  pressure  would  not  be  sufficient  to  ge- 
nerate these  currents.  Such  a  movement  of  the  moisture  in 
the  porous  layers  of  earth  would  also  take  place  from  the  colder 
and  damp  regions  to  the  hotter  and  dry  regions,  and  give  rise 
to  electric  currents  directed  in  the  same  direction.  The  free 
tension  of  the  thus  excited  electricity  could,  if  sufficiently 
strong,  make  itself  perceptible  in  the  electricity  of  the  air. 
In  this  respect  Secchi's  above-mentioned  researches  offer 
still  more  complete  material  for  the  decision  of  the  question  here 
stated. 
Two  telegraph-lines  were  constructed,  one  running  from  north 
to  south,  the  other  directed  from  east  to  west.  On  both  hourly 
observations  were  made  from  6  o'clock  in  the  morning  to  mid- 
night, from  June  1  to  16,  1863. 
The  following  are  the  results  of  these  observations : — 
1.  The  line  running  from  east  to  west  shows  much  stro  ger 
variations  than  the  north- south  line. 
2.  The  maxima  of  one  line  are  coincident  with  the  minima  of 
the  other ;  this  is  true  for  the  secondary  as  well  as  for  the  pri- 
mary turning-points.  The  chief  turning-points  are  at  7-8h  a.m. 
(minimum  of  north-south  and  maximum  of  the  east-west  line) 
and  11— 12h  at  noon  (maximum  of  north-south  and  minimum  of 
the  east- west  line). 
3.  During  the  night  the  currents  are  stronger  and  remain 
pretty  constant. 
Father  Secchi  draws  from  these  experiments  the  conclusion 
that  it  is  sufficient  to  observe  only  one  line,  and  limits  his  further 
