What kinds of figurative language does King use in his speech to decribe inequality and the work of the Civil Rights Movement?

He uses metaphors

"This sweltering summer of the Negro's legitimate discontent will not pass until there is an invigorating autumn of freedom and equality."

The opening of King's speech uses metaphors to compare the promises of freedom made in the Declaration of Independence, the Constitution and the Emancipation Proclamation and the failure of these documents to procure those freedoms for all. He then turns to a metaphor familiar to all-the weather.