IN LONDON IN 1907, Samuel Clemens walked through the lobby of his hotel dressed in a blue bathrobe and slippers. According to a story in the New York Globe, he "crossed Dover Street to the Bath Club, took his bath and returned to the hotel in the same unconventional garb."

Aware of the sensation he was creating, "Mr. Clemens coolly surveyed those who stared at him, and said he had done the same thing many times at the seaside in America."

When his action was chalked up to literary genius, it must've tickled the Twain in him.

Now comes National Geographic's show, "Mark Twain and Huck Finn: Joy-Flags and Milestones," to mark the 150th year of his birth, the 75th year of his death and the 100th anniversary of the publication of "Adventures of Huckleberry Finn." That ain't bad for a man who had mixed feelings about anniversaries -- as well the inventor of the telephone and the rest of the human race.

The walls here are filled with his irreverent sayings and exaggerations -- quotations chosen for their freshness. And there are at least a half-dozen museum phones set to play actors' recordings of his work, including the monologue about the man in the skiff meeting the great vessel, "The Begum of Bengal, 70 years out and homeward bound."

After a while one stops saying, "Wish I'd said that!" As Samuel Clemens/Mark Twain said, "A man will do many things to get himself loved, he will do all things to get himself envied." Twain must have, for he is both.

More than a funny man in a white suit, Mark Twain was a silver miner, a riverboat pilot and, we see here, an inventor -- of self- pasting scrapbooks and adjustable garters. He was a publisher and an entrepreneur who tended to see his writing as a sideline, channeling all the proceeds from "Huckleberry Finn" into the ill-conceived Paige typesetter. He declared bankruptcy, insisted on paying all his debts anyway, and did so with a round-the- world lecture tour -- in his "don'tcareadamn suit." The yellowing jacket of one is displayed here, moths having enjoyed a revered chunk near the formerly white lapel.

He was a great promoter, giving his name over to flour, cigars and shaving mugs. Here is an ad touting a hand-written "testimonial from a prominent writer, whose reputation, like that of the Wirt pen, is world wide." Mark Twain wrote, "With a single Wirt pen I carried the family's living for many years. With two, I could have grown rich."

Pages from original manuscripts show that he may well have done it all with one pen. He rarely scratched out; it seems he wrote entirely in his head.

Although to Twain a "classic" was "a book which people praise and don't read," he wrote a few himself about life on the Mississippi River. They are best read aloud. He also wroe some books most of us have never heard of -- and first editions of both kinds are displayed here in this lovingly done show, put together with the Mark Twain Memorial in Hartford, Connecticut.

This was Mark Twain -- but we can only glimpse Sam Clemens. On a lace tablecloth here, there is an arrangement of the sort that engulfs family pianos. Photos of wife, daughters, relatives and friends surround mementoes: Clemens' letter to his favorite daughter, Susy, at her birth; a letter he wrote to a friend at Susy's death; a silver epergne that decorated the Clemenses' wedding table; his top hat; a clip of his hair.

And no one can leave here without the source of Samuel Clemens' pen name being indelibly printed on the brain, courtesy of an infinitely looped film clip. In the movie version of "Life on the Mississippi," a river boatman throws a rope overboard to test the water's depth. When he finds the depth of two fathoms, safe for boat passage, he sings out, "Mark Twain!" MARK TWAIN AND HUCK FINN: JOY-FLAGS AND MILESTONES -- At the National Geographic's Explorers Hall through October 6.