A marvellous simile for the effect of a woman’s movements on a man’s heart.  I take it to mean her movements are as expansive in their effect on him as the tide on which his emotions bob like a cork, without any agency of its own. 

His heart danced upon her movements like a cork upon a tide.

See another Joyce metaphor for heart-moving emotions.

Source: James Joyce, A Portrait of the Artist as a Young Man (Harmondsworth: Penguin, 1964), p. 69

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