352     M.  F.  Zollner  on  the  Origin  of  the  Earth's  Magnetism, 
the  water  by  connecting  the  platinum  wires  melted  into  the  tube 
with  the  conductor  and  cushions  of  the  electrical  machine. 
In  turning  slowly  the  disk  of  the  electrical  machine,  a  move- 
ment of  the  particles  of  starch,  in  the  direction  of  the  positive 
current,  was  observed  near  the  walls  of  the  tube;  in  the  middle 
of  the  liquid  the  movement  was  in  the  opposite  direction.  It  was 
observed  by  a  microscope  magnifying  thirty  times.  If  the  in- 
tensity of  the  current  is  increased,  the  particles  in  the  middle 
of  the  tube  move  more  quickly,  while  the  larger  particles  near 
the  walls  change  their  direction  and  move  now  with  the  negative 
current.  Increasing  still  more  the  intensity  of  the  current,  all 
the  particles  move  in  the  direction  of  the  negative  current*. 
Constant  galvanic  currents  and  induction-currents  which  (by 
interrupting  the  communication  by  a  column  of  air)  are  always 
directed  in  the  same  sense,  act  similarly ;  the  particles  of  starch 
first  proceed  a  little  in  the  direction  of  the  positive  current,  turn 
suddenly  round  and  flow  quickly  in  the  opposite  direction. 
Using  wider  tubes,  a  stronger  current  is  necessary  to  produce 
the  motion  of  all  the  particles  of  starch  in  the  same  direction ; 
with  the  narrow  tubes  very  weak  currents  are  sufficient. 
These  facts,  which  are  described  in  detail  in  Wiedemann's 
*  Treatise  of  Galvanism  and  Electro-magnetism/  are  sufficient  to 
justify  the  assumption  that  all  streaming  motion  in  liquids,  especi- 
ally if  they  are  partly  in  contact  with  rigid  bodies,  is  accompanied  by 
electrical  currents  which  are  developed,  as  far  as  we  can  see  by  the 
facts  known  at  present,  chiefly  in  the  direction  of  the  flowing  liquids. 
7. 
Let  us  now  apply  these  facts  by  analogy  to  the  currents  in  the 
liquid  nucleus  of  the  earth  which  we  considered  above.  The  direc- 
tion of  the  upper  currents  in  the  northern  hemisphere  is  the  same 
as  that  of  the  trade- winds,  viz.  south-westerly.  Hence  the  di- 
rection of  the  electrical  current  produced  in  the  earth's  crust  is  a 
north-easterly.  We  must  look  on  the  inequalities  in  the  inner 
crust  of  the  earth,  which  are  continuously  touched  by  the  glow- 
ing liquid,  as  on  blocks  of  rock  which  on  the  bottom  of  the 
sea  or  of  mighty  rivers  are  always  influenced  in  one  direction 
by  the  flowing  water.  They  act  just  in  the  same  manner  as 
the  platinum  plates  do  in  the  experiments  of  Quincke.  The 
plate  touched  first  by  the  current  (the  westerly  projection)  cor- 
responds to  the  zinc,  the  plate  touched  last  (the  easterly  pro- 
jection) to  the  platinum  of  a  Grove's  battery.  Hence  the  cur- 
rent in  the  wire  (or  in  the  earth's  crust)  has  an  opposite  di- 
rection (i.  e.  from  east  to  west) . 
*  Pogg.  Ann.  vol.  cxiii.  p,  569  (1861). 
