  One set of the Ziolkowski family of exact solutions of the wave equation are
shown to represent pulses propagating with momentum smaller than energy/c. This
is explicitly demonstrated for special cases by calculating the total
electromagnetic momentum and energy. Since the ratio of momentum to energy is a
constant smaller than 1/c, there exists a Lorentz transformation to a frame in
which the total momentum is zero. In the zero-momentum frame the fields are
those of an annular pulse converging onto or diverging from a focal region.
