In the second paragraph of the speech (beginning with "five score years ago ..."), which extended metaphor does Dr. King introduce?

In the second paragraph
of this famous speech, Dr. King describes the Emancipation Proclamationthe document signed by
President Abraham Lincoln that freed all enslaved peoplesas a "great beacon light of
hope" to millions of enslaved individuals. Dr. King further describes the freedom it
promised as a "joyous daybreak" that would end the years and years of darkness and
oppression. Thiswhich compares freedom to light and oppression to darkness extends through these
few sentences. However, Dr. King goes on to use other powerful metaphors in this paragraph,
comparing discrimination and segregation to chains and manacles, like those which would have
bound slaves' hands and feet. He compares the material prosperity enjoyed by many whites to an
ocean while blacks continue to live in poverty, likened to lonely islands.