  We present discovery spectra of a sample of eight lensed galaxies at high
redshift, 3.7<z<5.2, selected by their red colors in the fields of four massive
clusters: A1689, A2219, A2390, and AC114. Metal absorption lines are detected
and observed to be blueshifted by 300-800 km/s with respect to the centroid of
Ly-alpha emission. A correlation is found between this blueshift and the
equivalent width of the metal lines, which we interpret as a broadening of
saturated absorption lines caused by a dispersion in the outflow velocity of
interstellar gas. Local starburst galaxies show similar behavior, associated
with obvious gas outflows. We also find a trend of increasing equivalent width
of Ly-alpha emission with redshift, which may be a genuine evolutionary effect
towards younger stellar populations at high redshift with less developed
stellar continua. No obvious emission is detected below the Lyman limit in any
of our spectra, nor in deep U or B-band images. The UV continua are reproduced
well by early B-stars, although some dust absorption would allow a fit to
hotter stars. After correcting for the lensing, we derive small physical sizes
for our objects, ~0.5-5 kpc/h for a flat cosmology with Omega_m=0.3,
Omega_Lambda=0.7. The lensed images are only marginally resolved in good seeing
despite their close proximity to the critical curve, where large arcs are
visible and hence high magnifications of up to ~20x are inferred. Two objects
show a clear spatial extension of the Ly-alpha emission relative to the
continuum starlight, indicating a ``breakout'' of the gas. The sizes of our
galaxies together with their large gas motion suggests that outflows of gas are
common at high redshift and associated with galaxy formation.
