Final answer:
The line "To find the mind's construction in the face" is spoken by King Duncan in Act 1, Scene 4 of Shakespeare's 'Macbeth', reflecting on deceit and appearances.
Step-by-step explanation:
The phrase "To find the mind's construction in the face" is spoken by Duncan in Act 1, Scene 4 of Macbeth. Duncan reflects on the inability to read a person's true intentions or character just by observing their facial expressions, remarking on how he had been deceived by the former Thane of Cawdor, whom he trusted deeply. This line is often cited to highlight the theme of appearance versus reality that permeates the play.