Last month, the Adirondack Nature Conservancy announced that it had inked a deal to buy Follensby Pond, near Tupper Lake. The pristine lake was once the site of the fabled “Philosopher’s Camp,” visited by Ralph Waldo Emerson. The group hopes the 14,000-acre parcel will eventually be added to the state forest preserve. Follensby has been off-limits to the public for more than a century. But last week, Brian Mann was invited to spend an autumn day paddling Follensby Pond. He was the first journalist to visit.