Why is the Plessy versus Ferguson decision an important landmark in the civil rights morament, even though Plessy was found guilty by the United States Supreme Court?

What is the rhyme scheme in this excerpt from longfellow's, "the tide rises, the tide falls? " (10 points) the tide rises, the tide falls, the twilight darkens, the curlew calls; along the sea-sands damp and brown the traveler hastens toward the town, and the tide rises, the tide falls.