[chi] = [chi]' - 4[pi][rho][theta](0) + 2[pi][rho][theta](z) +
+ 2[pi][rho][theta](z - c).
The surface-density of this stratum is [sigma] = c[rho]. The energy
per unit of area is
_
/ c
e = | [chi][rho]dz = c[rho]([chi]' - 4[pi][rho][theta](0)) +
_/0
_ _
/ c / c
+ 2[pi][rho]^2 | [theta](z)dz + 2[pi][rho]^2 | [theta](z - c)dz.
_/0 _/0
Since the two sides of the stratum are similar the last two terms are
equal, and
_
/ c
e = c[rho]([chi]' - 4[pi][rho][theta](0)) + 4[pi][rho]^2 | [theta](z)dz.
_/0