Mary Wollstonecraft Shelley? Robert Walton? Victor Frankenstein? Apocryphal?

Question for Quote Investigator: Finding a goal or purpose to strive for in life is wonderfully helpful; uncertainty and anxiety are replaced by mental tranquility. Mary Wollstonecraft Shelley who authored the groundbreaking science fiction novel “Frankenstein; or, The Modern Prometheus” once made this point. Would you please help me to find citation?
Reply from Quote Investigator: Shelley’s “Frankenstein” begins with the text of a letter from the explorer Robert Walton to his sister. The fictional Walton is leading an expedition toward the North Pole while hoping to make a major discovery such as a navigable passage connecting the Atlantic Ocean to the Pacific. Boldface added to excerpts by QI:1
These reflections have dispelled the agitation with which I began my letter, and I feel my heart glow with an enthusiasm which elevates me to heaven; for nothing contributes so much to tranquillize the mind as a steady purpose,—a point on which the soul may fix its intellectual eye. This expedition has been the favourite dream of my early years. I have read with ardour the accounts of the various voyages which have been made in the prospect of arriving at the North Pacific Ocean through the seas which surround the pole.
The 1818 edition employed the spelling “tranquillize”. Variant spellings include: tranquillise, tranquilize, and tranquilise.
Walton’s crew discover a man on a sledge who is nearly dead. The man is nursed back to health, and Shelley switches the narration of the novel. The rescued man is the ill-fated scientist Victor Frankenstein, and he recounts the rest of the tale.
Below are additional selected citations in chronological order.
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