PHILADELPHIA Curiosity about a line from "Hamlet" has led a University of Pennsylvania English professor to discover a tablet that was something of a Renaissance precursor of today personal digital assistants.

Teaching a Penn course on "The History of the Book in Early Modern Europe," Peter Stallybrass and history professor Roger Chartier were puzzled by a line in Shakespeare's "Hamlet."

Having seen the ghost of his father, Hamlet says:

Yea, from the table of my memory

I'll wipe away all trivial fond records,

All saws of books, all forms, all pressures past,

That youth and observation copied there. . .

In what kind of "table," or notebook, could one "wipe away" writing in the Renaissance? Lead pencils were only just being introduced, and the modern eraser did not exist. There was no obvious way to wipe ink off paper, which was the usual material for writing.

In the Folger Shakespeare Library in Washington, D.C., last week, Stallybrass found a miniature notebook with the title "Writing Tables with a Kalender for xxiiii. yeeres." Printed at the front of the book were the dates of fairs, tables of measurement, woodcuts of different kinds of coins and a description of England and Wales and, at the back, there were several blank pages coated with a substance that resembled plaster.

Stallybrass had read about a similar substance in Jessie Anne Owensbook, "Composers at Work," where she examined the slates and other erasable forms that Renaissance composers used for rough drafts. Now, here was one of the actual notebooks.

The "plaster" coating of the 1604 notebook, now peeling away in many places, contains the remains of a recipe, written in ink, which could probably be "wiped away" from this surface with, for instance, a sponge. This appears to be exactly the kind of notebook that Hamlet imagines when he compares his mind to "tables" from which all writing could be "wiped away."

It's probable, Stallybrass said, that there were tens of thousands of "Writing Tables" in Shakespeare's lifetime in addition to the best-selling almanacs that often included blank sheets for keeping notes and accounts.

But the problem remains, how common are the erasable surfaces that would have been added after the book was printed?

It's too early to give a complete answer to that, but other erasable surfaces are already being discovered by the Folger Frank Mowery, including a copy of the "Writing Tables" with specially treated parchment at the back. And Roger Chartier, StallybrassPenn colleague, has discovered several French references to "prepared paper," including one detailed recipe for making an erasable surface.

So Hamlet wasn't the only person in the Renaissance to imagine a notebook in which the writing could be "wiped away."