"One of the things that appeals to me in working on the books is the sense of adventure in searching for these natural treasures," said Dunn, who divides his time between a home in Albany and a camp on the Great Sacandaga Lake, 40 miles to the northwest in the Adirondack foothills.

"I've always collected old postcards, and it's fun to have one of a waterfall that was very popular in Victorian times and try to find it again," Dunn said. "It's exciting to find a beautiful place people have lost track of over the years. Of course, we've also been to many desolate gorges and ravines looking for waterfalls, only to come up with nothing."

Dunn includes old postcard pictures of waterfalls as illustrations in his books.

The popularity of waterfalls is evident in the large number of Web sites devoted to them on the Internet. One site, the World Waterfall Database, seeks to catalog the world's most significant waterfalls and rate them according to size, beauty and other factors.

"I'm not certain just what quality a waterfall possesses that intrigues me so," writes Dean Goss of Jericho, Vt., co-creator of the World Waterfall Database. "Maybe I like the sound, maybe I like the geometry, perhaps I am awed by the power water has over rock, perhaps the negatively charged ions that remove impurities from the air has something to do with it."

The sound of a waterfall has much to do with its appeal, Dunn said. Like the wind howling through hemlocks or waves pounding on the shore, "waterfalls are the voice of nature, powerful and majestic, beckoning and mesmerizing," he writes in "Hudson Valley Waterfall Guide."

And they offer an ever-changing show over the seasons: splashing into pools reflecting brilliant foliage in the fall, freezing into dramatic blue pillars in winter, surging with fury in the spring, and trickling languidly over mossy ledges in midsummer.

"I think people today have the same reaction to waterfalls as the Victorians did," Dunn said. "We're fascinated by the sublime and the awesome, mesmerized by these entities of rock and water."