Journal 1840
p10“A very slight passage in Zimmerman would be my key.”
Fuller, Margaret. "Journal 1840." Houghton Library, Harvard University; bMS Am 1086 (85); Box 5 (85).
Inferred Fuller mentions 'a very slight passage in Zimmerman' as her 'key' to a Petrarch project; the work is not named, but Zimmermann's primary and best-known work was On Solitude, which extensively treats Petrarch. Title inferred as On Solitude since no other Zimmermann work is known to engage with Petrarch in a way that matches Fuller's description.