A note to Sir Thomas Browne's Vulgar Errors, Book V, Chapter 18
Images of St. Jerome with time-keeping devices may be found at The Web Gallery:
Among the more famous examples of portraits of Jerome, see Antonella da Messina's St Jerome in his Study, where the lion (in the on-line version) is a dark smudge walking around in the corridor to the viewer's right. For some others, see The Web Gallery's search engine.
For many years this page read as follows:
I have yet to find a portrait of Jerome with a clock. The most famous painting which (at least tangentially) associates Jerome with a clock is Botticelli's pendant to the Ghirlandaio above, a St. Augustine which most definitely has a clock (see the detail here; as long as you're there, note the position of the hand at the bottom, or midnight; note also that the clock moves counter-"clockwise"). The depiction relates to St Augustine's miraculous knowledge of the death of St Jerome at the moment of its occurrence (this miracle was painted by Carpaccio).
Now, however, through the courtesy and alertness of Yves Breugelmans, who knew of my interest in Jerome's clock, we've found one, hanging in the Musée Comptadin-Duplessis of Carpentras in southern France; bearing catalogue number 204, a 16th-century painting by an anonymous artist, titled St-Hieronymus:
Photo © Yves Breugelmans 2008; by kind permission
On Jerome in general, see the article in the Catholic Encyclopedia (not in some respects up to their usual standards).
This page is maintained at the University of Chicago by James Eason, who welcomes comments, criticism, and suggestions.