  Dispersion corrections to elastic electron scattering from $^{208}$Pb at
energies up to 150 MeV are estimated within the second-order Born
approximation. All strong transient nuclear excited states with angular
momentum up to $L=3$ and natural parity are taken into consideration. It is
found that at small scattering angles the high-lying $L=1$ isovector states
provide the dominant contribution to the dispersive change of the differential
cross section and of the beam-normal spin asymmetry. At the backmost angles
these changes are considerably smaller and are basically due to the isoscalar
$L=2$ and, to a lesser extent, $L=3$ states. In comparison with the findings
for $^{12}$C, the dispersive cross-section modifications for $^{208}$Pb are
significantly larger, while the spin-asymmetry changes are much smaller at all
angles. The latter originates from the destructive interference of the
multipole contributions in $^{208}$Pb that switch sign when proceeding from $L$
to $L+1$. This mechanism might be the origin of the small beam-normal spin
asymmetries recently measured in ${}^{208}$Pb at much larger energies.
