«=Ig— L-

The  maximum  of  the  direct  currents  ("break")  is  I,  and

that  of  the  inverse  (or  "make")  is  -.    If  we  wish  to  know  at

the  end  of  what  times  t  and  t'  the  strengths  of  the  two  induced

currents  y  and  z  are  reduced  to  —  of  that  of  the  primary  we

m


242  MUTUAL  AND  SELF  INDUCTION

obtain  by  substitution  of  —  for  y  and  ;:  in  the  two  above  equa-
m

tions  the  following : —

1       -^^

__  =  e    l'    for  the  direct-induced  current,

m

and  —  =  ^   sL  for  the  inverse-induced  current,

m     2


and  therefore  i'  =  2  (^1  -  ]^^).
t         \       loff  m/


log?

We  see  that  t*  is  always  greater  than  «,  and  that,  in  propor-
tion as  m  increases,  f  tends  towards  a  limit  2  t,  or  the  inverse
current  has  a  duration  about  double  that  of  the  direct  secondary.
We  shall  now  see  how  this  theory  is  confirmed  by  experiment.
§  7.  Oompariflon  of  Theory  and  Experiment. — Masson  and
Bregaet  carried  out  a  series  of  experimental  researches  on  induced
currents  which  illustrate  and  confirm  the  foregoing  theory.
