CAMBRIDGE, MASS. -- Two pieces of paper discovered glued inside a book at Harvard University's Houghton Library have provided a window on the past: The 500-year-old pieces of paper printed in German turned out to be most of a 15th-century almanac.

The two yellowed sheets folded four times are eight pages of a 12-page almanac for Krako'w, Poland, published in 1493. Chronicling the prospects for 1494, the almanac predicted weather, planetary eclipses and the astrological fates.

"It's not earth-shattering," James Walsh, whose title is keeper of printed books, said recently of his discovery. "Yet it is something to have assembled something printed that never was known before.

"Just as we throw away our calendar for 1987 when 1988 comes along, so they threw away their almanacs," he said. "They're as a result quite rare."

Walsh found the pages at the start of a much bigger scholarly expedition. Since July 1986, he has been compiling a catalogue of Harvard's 4,000-volume collection of books published before 1501.

The technical term for such books is "incunabula." Derived from the Latin word meaning cradle, incunabula were published in the infancy of printing, which began in the mid-1400s with the Gutenberg Bible.

According to the Houghton's chief librarian, Lawrence Dowler, Walsh is one of the few people in the world capable of the massive and unprecedented undertaking because of his background in Latin and Greek.

Walsh expects to be finished in another five years. The fruits of his work will become the several-volume "Catalogue of Incunabula in the Harvard University Library." The State University of New York at Binghamton will publish the volumes.

The almanac pages Walsh found were recycled as book lining, a common 15th-century practice for disposing of misprinted and outdated material. The sheets were inside the front and back covers of a copy of Justinian's "Institutiones" belonging to the Harvard Law School.

The pages were removed by Marjorie Cohn, conservator of Harvard's Fogg Art Museum. When Walsh realized he had a nearly complete book, he searched for the rest of it. A catalogue of such ancient materials led him to the missing pages at the Huntington Library in San Marino, Calif.

The librarians exchanged photocopies of their treasures. Walsh said he plans to bind the photocopies with his pages to make a facsimile of the original.

When the catalogue is completed, the almanac will go on exhibit.

In the meantime, Walsh hopes to find more treasures buried in the pages of the distant past.

"I have seen other leaves like that, but usually they're for very large books and trying to identify them would be difficult and would take too much time," he said. "What was interesting about this was, I could see I had almost the whole thing. Maybe in the next few years I will turn up more."