It was two decades ago, during a tour of the British Museum in London, that Harold and Peggy Osher decided to seize history.

More precisely, the couple were so exhilarated by a map collection they'd just seen that they walked to a nearby shop and bought two old renderings of their home state of Maine. One cost the equivalent of $20, the other $200."I'm a history and geography freak," explained Harold Osher, a cardiologist who, with his wife, went on to collect more than 1,000 individual maps and more than 10,000 more in books during the next 20 years - including a 1482 German woodcut of the world for which he spent about $85,000.

A stunning example of what the Oshers have accumulated goes on display at the University of Southern Maine Monday to mark Patriots Day, which commemorates the start of the Revolutionary War and is observed only by this state and Massachusetts.

Included in the collection is a map that is one of only two copies of an original used to end that war during the Treaty of Paris.

Cartographers view the original as the most important map in North American history, and its few remaining copies are considered nearly as significant. The initial map, drawn by a botanist named John Mitchell in 1775, is in the British Library; an 1897 copy is in the National Archives; and the final version of 1898, measuring 41/2 feet by 61/2 feet, hangs at the Osher Map Library and Smith Center for Cartographic Education.

The maps contain such extensive detail that they have been used as recently as the 1980s. At that time, the copy that Osher bought at an auction in Boston last year (for $60,000) was used for negotiations with Canada over fisheries in the Gulf of Maine.

"It is a treasure," Matthew Edney, an associate professor at the University of Maine and the resident map scholar at the Osher Map Library, said of the Mitchell map copy here. Edney, whose considerable enthusiasm for maps rivals Osher's, added that "in terms of history, it's a culmination, it's the best, most comprehensive map of the 19th century."

Though Osher has spent a sizable amount of cash for his maps - he prefers not to discuss how much but estimates it's in the millions - there's no mistaking that his obsession has little, if anything, to do with money. Indeed, far from perceiving their acquisitions as an investment, the Oshers have donated them all to the University of Southern Maine.

Moreover, the Oshers tied strings to their contribution: Unlike other map collections in this country, which typically are stored for use by specialists and for occasional displays, this one must be exhibited and made available to anyone who wants to view or study the maps. Local grade-school children, along with students at the university itself, reportedly have been the most ardent fans since the facility opened in the fall of 1995.

Osher acknowledged that most people fail to share his appreciation for maps. But, with evident pride, he expressed the hope that his collection is helping to change that.

"We've opened a lot of eyes," he said. "A class of fifth-graders comes in here and sees a map of Captain Smith's, or a book with Pocahontas or even her picture, and they can't get enough of it. It makes history come alive."

Osher attributed much of his own fervor for map collecting to this notion of gaining a more-complete, visual sense of history. In that regard, he said, his hobby is much like his profession, in which he also relies on graphic displays - in X-rays, for example - for critical information.

Osher's soft-spoken manner sometimes belies the ardor with which he has pursued his 20-year obsession with purchasing and meticulously studying maps.

It's no coincidence, he explained, that his retirement as director of cardiology at the Maine Medical Center in 1989 coincided with his decision to begin donating his collection to the map museum. And this is how he described the revelation that he wanted to spend his life in the world of cartography: "I began to know the meaning of lust."