502     M.  F.  Zollner  on  the  Origin  of  the  Earth's  Magnetism. 
troduced  into  the  water.  They  were  placed  in  the  sides  of  two 
T-shaped  glass  tubes,  so  that  the  flowing  water  could  not  touch 
them.  The  two  T-shaped  tubes  were  united  by  a  gutta-percha 
tube  1220  millims.  long,  so  that  the  length  of  the  column  of 
water  was  now  about  3*2  times  as  great  as  in  the  first  experi- 
ments.   The  following  Table  shows  the  results : — 
"Water  not  flowing.         Water  flowing.  Difference. 
399-0  3830  -160 
3990  3830  -160 
Current  of  water  reversed  : — : 
Water  not  flowing.        Water  flowing.  Difference. 
398-5  413-0  +14-5 
398-5  412-5  + 140 
The  direction  of  the  electric  current  was  always  the  same  as 
that  of  the  current  of  water. 
In  order  to  attain  an  approximate  value  for  the  electromo- 
tive force,  I  introduced  into  the  quiet  water  a  current  of  one  of 
Grove's  cells  ;  I  observed  a  deflection  of  60°.  Hence  the  elec- 
tromotive force  produced  by  the  flow  of  a  current  of  water  1220 
millims.  long  was  about  the  fourth  part  of  that  of  a  Grove's  cell. 
I  suspect  that  the  cause  of  these  currents  is  the  same  as  that  of 
the  currents  observed  by  Quincke.  If,  therefore,  Quincke  in  his 
first  paper,  "'On  a  new  Class  of  Electrical  Currents,"  says  (p.  13), 
"When  the  tubes  were  fixed  together  without  diaphragm,  no 
deflection  of  the  galvanic  needle  was  observed  ;  we  see,  therefore, 
that  the  diaphragm  is  necessary  for  the  production  of  the  electric 
current,"  the  cause  of  the  failure  is  probably  that  the  column  of 
water  was  too  small,  and  most  likely  insulated. 
I  believe  thatAdie*  in  the  above-mentioned  experiment  (p.  350) 
has  observed  those  electrical  currents  which,  as  I  hope  to  prove  by 
the  above  and  other  experiments,  are  necessarily  connected  with 
every  streaming  motion;  for  the  moving  forces,  acting  upon 
the  elements  of  a  flowing  mass  of  liquid,  are  not  in  equilibrium 
as  long  as  the  movement  takes  place,  and  I  am  inclined  to  look 
at  the  partial  difference  in  pressure  existing  in  the  direction  of 
the  currents  as  the  cause  of  the  electrical  currents.  Experience 
shows  that  wherever  such  differences  are  called  forth  in  bodies, 
they  may  become  the  source  of  electricity  by  adequate  combi- 
nation and  under  suitable  conditionsf. 
*  Adie  tries  to  explain  the  currents  observed  by  him  by  the  influence  of 
the  oxygen  of  the  atmosphere,  according  to  the  analogy  of  gas-batteries. 
He  says  in  the  paper  cited,  p.  383,  "  With  both  plates  in  still  water  and  a 
tube  filled  with  oxygen  inverted  over  one,  the  effect  was  the  same." 
\  The  manuscript  of  the  Appendix  was  delivered  to  the  printers  on  Fe- 
bruary 13,  1872. 
