ON  DYNAMIC  OR  VOLTAIC  ELECTRICITY.  259 
The  rubber  is  frequently  much  adulterated  by  the  addition  of 
tapioca  or  sand,  to  increase  its  weight ;  and  unless  care  is  taken 
in  its  manufacture,  It  will  have  many  cells  containing  air  and 
water.  Water  is  seen  to  exude  from  nearly  all  of  it  when  cut, 
which  is  always  done  for  the  purpose  of  examination  before  pur- 
chase. I  brought  home  some  specimens,  that  were  more  than 
half  mud."  Pages  330  and  331. 
IDENTITY  OF  DYNAMIC  OE  VOLTAIC  ELECTKICITY  WITH 
STATIC  OR  FRICTIONAL  ELECTRICITY. 
By  Professor  Faraday.* 
The  Friday  evening  meetings  for  the  season  commenced  at  the 
Royal  Institution  on  Friday  last,  the  opening  lecture  being  deliv- 
ered by  Professor  Faraday  to  a  very  crowded  audience.  The 
subject  was  the  developement  of  electrical  principles  produced  by 
the  working  of  the  electric  telegraph.  To  illustrate  the  subject, 
there  was  an  extensive  apparatus  of  voltaic  batteries,  consisting 
of  450  pairs  of  plates,  supplied  by  the  Electric  Telegraph  Com- 
pany, and  eight  miles  of  wire,  covered  with  gutta  percha,  four 
miles  of  which  in  coils  were  immersed  in  tubs  of  water,  to  show 
the  effects  of  submersion  on  the  conducting  properties  of  the  wire 
in  submarine  operations.  The  principal  point  which  Professor 
Faraday  was  anxious  to  illustrate,  was  the  confirmation  which 
experiments  on  the  large  scale  of  the  electric  telegraph  have  af- 
forded of  the  identity  of  dynamic  or  voltaic  electricity  with  static 
or  frictional  electricity.  In  the  first  place,  however,  he  exempli- 
fied the  distinction  between  conductors  and  non-conductors,  im- 
pressing strongly  on  the  audience  that  no  known  substance  is 
either  a  perfect  conductor  of  electricity  or  a  perfect  non-con- 
ductor, the  most  perfect  known  insulator  transmitting  some 
portion  of  the  electric  fluid,  whilst  metals,  the  best  conductors, 
offer  considerable  resistance  to  its  transmission.  Thus  the  copper 
wire  of  the  submarine  electric  telegraph,  though  covered  with  a 
thickness  of  gutta  percha  double  the  diameter  of  the  wire,  permit 
an  appreciable  quantity  of  the  electricity  transmitted  to  escape 
through  the  water ;  but  the  insulation  is,  nevertheless,  so  good 
*  From  the  London  Mechanics'  Magazine,  January  7. 
