What is the is the significance of Carton's comparing himself to the eddy?
The quote is found in Chapter 9 of Book Three of A Tale of Two Cities and goes on to say, "When he awoke and was afoot agian, he lingered there yet a little longer, watching an eddy that turned and turned purposeless, untill the stream absorbed it, and carried it on to the sea--'Like me!"
After Sydney Carton visits the shop of the chemist, he carries a little child across a street through the mud; then, through the quiet streets, Carton hears the "echoes of his feet" as he wanders along the Seine near the Ile de la Cite. For a time Carton falls asleep; then, when he awakens he watches an eddy that is carried by the "stream" out to the sea and likens it in its purposelessness to himself.
This passage of Chapter IX of Book the Third is significant because it brings together two motifs of the novel: the echoing footsteps that presage the Revolution and the pursuance of fate, with the metaphor of the rising sea as the surging bloodlust of the bonnets rouges of the Revolution which are introduced in Chapter XXI and XXII of Book the First respectively. In Chapter XX, for instance, Dickens writes,
But, there were other echoes, from a distance, that rumbled menacingly in the corner all through this space of time. And it was now, about little Lucie's sixth birthday, that they began to have an awful sound, as of a great storm in France with a dreadful sea rising.
Certainly, there is much foreshadowing in Sydney Carton's reflections upon his misdirected life that once showed signs of brillance as in his youth and the trial of Charles Darnay and his consultations provided to Stryver, the "lion." For, his potential greatness has now been washed away by his libation and his lack of self-direction, much like the eddy that crests large and spectacular, but fades and dissipates into the sea. Perhaps, even Carton's own life may travel the route of the river and also be swept away.