\magnification=\magstep2

$$
\eqalign{
(L_1 - L_2) &= \quad N \lambda \qquad\qquad\quad\quad {\rm bright\ spot} \cr
(L_1 - L_2) &= (N + {{1}\over{2}}) \lambda \qquad\qquad 
             \thinspace\thinspace {\rm dark\ spot} \cr
}
$$

$$
{{\Delta L}\over{L}} = \thinspace \alpha \thinspace
           {\Delta} T
$$

\bye
