\magnification=\magstep2

$$
dI = - \kappa \thinspace \rho \thinspace I \thinspace ds 
$$

$$
\eqalign{
{ {\int { {dI}\over{I}} } }   &=   - { {\int_0^s \kappa \rho ds } } \cr
  { \ln(I / I_0) }            &=   - \kappa \rho { {\int_0^s ds } } \cr
                              &=   - \kappa \rho s \cr
}
$$

$$
\eqalign {
{ {I}\over{I_0} } &= e^{- \kappa \rho s} \cr
                  &= e^{- s / \ell} \cr
}
$$

$$
\eqalign {
{ {I}\over{I_0} } &= e^{- \kappa \rho s} \cr
                  &= e^{- \tau } \cr
}
$$

\vfill\eject

$$
I(X) = I_0 e^{-c X}
$$

$$
m(X) = m_0  + kX
$$


\bye
