I am currently reading The House of Seven Gables by Nathaniel Hawthorne. To my surprise, progress is a spiral was mentioned by the character Clifford. I thought I would share:
"You are aware, my dear sir,--you must have observed it in your own experience,--that all human progress is in a circle; or, to use a more accurate and beautiful figure, in an ascending spiral curve. While we fancy ourselves going straight forward, and attaining, at every step, an entirely new position of affairs, we do actually return to something long ago tried and abandoned, but which we now find etherealized, refined, and perfected to its ideal." (page 270)
I found that so interesting and wanted to share.