Answer:
In the third paragraph of the excerpt, Douglass uses the figure of speech called "personification." He describes the ships on the Chesapeake Bay as "so many prison-houses." This means that Douglass sees the ships as being like prisons because they are used to transport slaves to other parts of the country where they will continue to be enslaved. The use of personification indicates an important turning point in Douglass's life because it shows how he has come to view the world around him in a new and more profound way. By seeing the ships as prisons, he recognizes the full extent of the horrors of slavery and the dehumanizing effect it has on both the enslaved and the enslavers.