'Humor," James Thurber once said, "is a serious thing. I like to think of it as one of our greatest and earliest national resources which must be preserved at all costs." Indeed, Americans have, since Benjamin Franklin's Poor Richard's Almanac , prided themselves on the ability to laugh both at and with themselves, even in the worst of times. Not to laugh is to give up hope. No test of that ability could have been greater than The Great Crash of 1929.

This week marks the 50th anniversary of that Black Thursday, and on Thursday the National Portrait Gallery will commemorate that infamous day with an exhibit focusing on the personalities and events of the crash. Included will be 34 political cartoons, some of which are shown here, lent to the gallery by the New York Stock Exchange and seldom seen since they were first published in newspapers and magazines of the day.

From San Francisco to Des Moines to New York City, the cartoonists of the crash and its aftermath echoed Mark Twain's statement that "the secret source of Humor itself is not joy but sorrow," often sorrow at our own human folly. And, like all good artists, these seers often saw our folly before we saw it ourselves.

The work of these cartoonists, like Twain's, made America laugh through her tears. It still does.