THE 
LONDON,  EDINBURGH,   and  DUBLIN 
PHILOSOPHICAL     MAGAZINE 
AND 
JOURNAL   OF   SCIENCE. 
[FOURTH   SERIES.] 
JANUARY  1872. 
I.  Electrodynamic  Measurements.  By  Professor  "Wilhelm 
Weber. — Sixth  Memoir,  relating  specially  to  the  Principle  of 
the  Conservation  of  Energy* . 
THE  law  of  electrical  action  announced  in  the  First  Memoir 
on  Electrodynamic  Measurements  {Elektrodynamische 
Maassbestimmungen,  Leipzig,  1846)  has  been  tested  on  various 
sides  and  been  modified  in  many  ways.  It  has  also  been  made 
the  subject  of  observations  and  speculations  of  a  more  general 
kind ;  these,  however,  cannot  by  any  means  be  regarded  as  having 
as  yet  led  to  definite  conclusions.  The  First  Part  of  the  follow- 
ing Memoir  is  limited  to  a  discussion  of  the  relation  which  this 
law  bears  to  the  Principle  of  the  Conservation  of  Energy,  the 
great  importance  and  high  significance  of  which  have  been 
brought  specially  into  prominence  in  connexion  with  the  Mecha- 
nical Theory  of  Heat.  In  consequence  of  its  having  been  asserted 
that  the  law  referred  to  is  in  contradiction  with  this  principle, 
an  endeavour  is  here  made  to  show  that  no  such  contradiction 
exists.  On  the  contrary,  the  law  enables  us  to  make  an  addition 
to  the  Principle  of  the  Conservation  of  Energy,  and  to  alter  it 
so  that  its  application  to  each  pair  of  particles  is  no  longer 
limited  solely  to  the  time  during  which  the  pair  does  not  undergo 
either  increase  or  diminution  of  vis  viva  through  the  action  of 
other  bodies,  but  always  holds  good  independently  of  the  mani- 
fold relations  to  other  bodies  into  which  the  two  particles 
can  enter. 
Besides  this,  in  the  Second  Part  the  law  is  applied  to  the  de- 
*  Translated  by  Professor  G.  C.  Foster,  F.R.S.,  from  the  Abliandluiujen 
der  mathem.-phys.  Classe  der  Konigl.  Sachsischen  Gesellschaft  der  Wis- 
senschaften,  vol.  x.  (January  18/1). 
Phil.  Mag.  S.  4.  Vol.  43.  No.  283.  Jan.  1872.  B 
