The ill-fated mountaineer George Mallory's only book was "Boswell the Biographer"?
Jacoba Helena de Vicq - Madame de Zuylen
Jacoba Helena de VicqBorn 1724
Boswell first mentions "cultivating her acquaintance" on December 16, 1763.1
Full name sometimes given as Helena Jacoba de Vicq.
Note 1: Although he only refers to a Madame de Zuylen (which could also be her daughter), it seems reasonable to suggest that it was indeed Jacoba Helena de Vicq he was referring to.