498       M.  F.  Zollner  on  the  Origin  of  the  Earth's  Magnetism, 
was  found  that  small  movements  in  the  horizontal  intensity  of  the 
terrestrial  magnetism  coincided  with  simultaneous  small  changes 
of  the  current  in  the  line  running  from  east  to  west. 
When  magnetic  instruments  and  galvanometers  of  greater 
sensitiveness  were  employed,  a  complete  analogy  was  found  to 
exist  between  the  current  in  the  wire  running  from  east  to  west 
and  the  intensity,  and  then  between  the  current  of  the  wire  running 
from  north  to  south  and  the  dip.  Moreover  it  was  found,  by  com- 
parison of  the  movements  in  the  wires  which  were  stretched 
along  the  astronomical  and  magnetical  meridians,  that  the  move- 
ment of  the  earth-current  takes  place  chiefly  parallel  with  the 
equator. 
Already,  before  these  observations  of  Lamont's,  Walker*  had 
occupied  himself  with  similar  researches,  which,  however,  chiefly 
referred  to  the  great  and  extraordinary  movements  of  the  earth- 
current,  and  were  therefore  made  on  the  telegraph-lines.  He 
found  that  the  earth-current  was  directed  from  north-east  to 
south-west,  or  vice  versa,  and  in  a  line  inclined  at  an  angle  of 
41 1°  to  the  astronomical  meridian. 
It  is  remarkable,  however,  that  in  telegraph-lines  lying  in  the 
same  direction  the  earth-current  is  not  always  equally  intense; 
some  lines  are  even  found  in  which  the  earth-current  never 
shows  great  intensity. 
Very  extensive  researches  on  the  earth- current  have  been 
made  by  Matteuccif  and  SecchiJ. 
Matteucci  laid  two  wires  covered  with  gutta  percha,  each  6 
kilometres  long,  one  in  the  magnetic  meridian,  the  other  in  a 
direction  at  right  angles  to  it.  At  the  ends  ditches  of  2  metres 
depth  were  sunk.  In  the  middle  of  each  ditch  a  hole  of  \  cubic 
metre  was  made,  the  sides  of  which  were  covered  with  clay,  and 
filled  with  water.  Porous  vessels  filled  with  a  saturated  solu- 
tion of  sulphate  of  zinc  were  then  placed  in  these  holes,  in 
which  well-amalgamated  zinc  plates  were  laid  which  were  in 
communication  with  the  wires.     In  this  manner  the  plates  were 
*  "  On  Magnetic  Storms  and  Earth-currents."  Proceedings  of  the 
Royal  Society,  vol.  xi.  pp.  105-11 1 ;  Phil.  Trans.  1861,  pp.  89-131.  Other 
Literature  in  1861: — 
H.  Lloyd,  "  On  Earth-currents  and  their  Connexion  with  the  Pheno- 
mena of  Terrestrial  Magnetism,"  Phil.  Mag.  Ser.  4.  vol.  xxii. 
B.  Stewart,  "  On  the  great  Magnetic  Disturbance  of  August  28  to  Sep- 
tember 7,  1859,  as  recorded  by  Photography  at  the  Kew  Observatory," 
Proceedings  of  the  Royal  Society,  vol.  xi. 
Airy,  "  On  Spontaneous  Terrestrial  Currents,"  Reports  of  Brit.  Assoc. 
1861  and  1862. 
t  "  Sur  les  Courants  Electriques  de  la  Terre,"  Comptes  Rendus,  tome 
lviii.  p.  942  et  seqq.  (1864). 
\  "  Sur  les  Courants  de  la  Terre  et  leur  Relation  avec  les  Phenomenes 
Electriques  et  Magnetiques,"  Comptes  Rendus,  tome  lviii.  p.  1181  et  seqq. 
