238  Intelligence  and  Miscellaneous  Articles. 
early  rocks,  and  showed  that,  with  the  exception  of  the  Brachiopods, 
Sponges,  and  the  smaller  Crustacea,  the  range  was  very  limited. 
A  description  of  the  various  beds  forming  the  Cambrian  rocks  of 
St.  David's  was  also  given,  and  proofs  adduced  to  show  that  fre- 
quent oscillations  of  the  sea-bottom  took  place  at  this  early  period, 
and  that  the  barrenness  of  some  portions  of  the  strata,  and  the  rich- 
ness of  other  parts,  were  mainly  attributable  to  these  frequent  changes. 
XXIX.  Intelligence  and  Miscellaneous  Articles. 
ON  SIGNALS  OBSERVED  IN  A  WIRE  JOINING  THE  EARTH-PLATES 
IN  THE  NEIGHBOURHOOD  OF  A  THIRD  EARTH-PLATE  USED  FOR 
A  TELEGRAPHIC  CIRCUIT.  BY  G.  K.  WINTER,  TELEGRAPH 
ENGINEER,  MADRAS  RAILWAY. 
TN  the  course  of  some  experiments  on  earth-currents  an  effect  was 
-*■  observed  which  has  led  to  the  discovery  of  a  fact  which  may  be 
of  some  practical  value,  besides  throwing  additional  light  upon  the 
part  played  by  the  earth  in  telegraphic  circuits. 
Although  several  telegraph-wires  pass  through  Arconum,  only 
two  are  terminal  at  that  station, — one  connecting  it  with  Cuddapah, 
a  town  lying  120  miles  to  the  north-west;  and  the  other,  which  is 
very  little  used,  connects  it  with  Conjeveram. 
Two  earth-plates  were  imbedded  in  the  ground  in  a  line  running  east 
and  west  and  nearly  radial  to  the  office  earth-plate ;  they  were  about 
a  quarter  of  a  mile  apart,  and  the  nearest  was  about  the  same  distance 
from  the  office  plate.  A  wire  was  erected  on  separate  poles,  connect- 
ing the  two  experimental  earth-plates.  When  a  reflecting  galvano- 
meter, similar  to  those  used  for  cable  signalling,  was  inserted  in  this 
circuit,  there  was  a  pretty  strong  deflection  ;  but  riding  on  this  de- 
flection, as  it  were,  were  distinct  signals,  which  were  ultimately,  on 
comparison,  found  to  agree  perfectly  with  the  signals  passing  in  the 
Cuddapah  wire. 
The  experiments  were  made  in  a  building  at  least  150  yards  from 
the  telegraph  office ;  and  the  poles  carrying  the  experimental  wire 
were  at  least  that  distance  from  those  carrying  the  Cuddapah  wire. 
It  is  utterly  impossible,  therefore,  that  any  accidental  leakage  could 
account  for  the  signals.  On  other  wires  running  in  other  directions 
and  varying  from  one  to  two  miles  in  length,  the  same  effects  were 
observed ;  so  that  the  currents  going  to  earth  at  the  office  earth- 
plate  must  radiate  from  it  through  the  earth,  and  the  signals  in  the 
experimental  wires  must  have  been  derived  from  these  radiations. 
The  signals  I  have  now  made  perfectly  legible  by  using  a  thick 
wire  reflecting  galvanometer,  filling  the  mirror-chamber  with  water 
to  steady  the  needle  and  mirror. 
I  have,  in  conclusion,  to  express  my  thanks  to  Mr.  Lundy,  of  the  Bri- 
tish Indian  Extension  Telegraph  Company,  for  having  kindly  lent  me 
a  reflecting  galvanometer  and  one  of  his  staff  accustomed  to  read  by 
the  mirror.  I  may  also  mention  that,  when  speaking  to  him  on  the 
subject  of  the  signals  I  had  observed,  he  said  he  thought  they  were 
due  to  a  wire  that  was  terminal  at  Arconum.  I  was  myself  of  the 
same  opinion,  but  had  not  at  the  time  actually  made  the  comparison. 
Arconum,  Jan.  27,  1872. : 
