TRAVEL INSIDER : Travel 101: A Timeline of American Tourism : Exhibits: ‘Americans on Vacation’ traces the history of leisure excursions from the stagecoach era to the jet.

Today, travelers, a few words on your probable ancestry. If you spend much of your free time on the road, or in the air, or merely between the pages of this section, you are spiritual heir to Mrs. Mildred Cramer of Flint, Mich.

The curators of the Henry Ford Museum in Dearborn, Mich., discovered Mrs. Cramer about five years ago, early in their work on the first major museum exhibit to trace the history of American leisure travel. The exhibit, “Americans on Vacation,” recently arrived at the Museum of San Diego History, and will remain there until Aug. 25.

Mrs. Cramer was married to a salesman, and the two were on the road together a lot in the early 1930s. Mrs. C. documented their summertime travels with astonishing care. She hoarded postcards, clipped out snatches of magazine stories, mounted ticket stubs, and artfully arranged whatever two-dimensional evidence came to hand. Enjoying the high life in Mexico and Cuba during Prohibition, she paused to peel liquor labels from her bottles, and later smoothed them onto scrapbook pages.

The scrapbooks are quintessential tourist artifacts. And “Americans on Vacation” is a modest but provocative analysis of the tourist’s lot in life, illustrated with such artifacts as a surfboard-bearing 1940 Ford Woody.

In the exhibit’s luggage display, smallish stage coach “carpet-bags” give way to massive wooden steamer trunks, which in turn give way to leather railroad baggage, which neighbors the lightweight plastic luggage designed to airline weight limits.

Not all the history is cheery. In the exhibit catalog, alongside photos of private railroad cars and transatlantic cruises, co-curators Donna R. Braden and Judith E. Endelman show a Virginia “picnic grounds for Negroes” in 1940, and the “colored waiting room” of a Georgia railroad station in 1938.

Noting the universal pattern of vacations through the ages, the curators plotted their display in four parts: planning, getting there, being there, and remembering it all. Together, they make up a strange stew of technological advances, social movements and commercial strategies.

The starting point, more or less, is American independence in 1776, when only the richest Americans took vacations, usually grand Continental tours.

When I called her in Michigan, Judith Endelman spoke of those days as if they were pre-Columbian history.

“A gentlemen, to become educated, might take up to a year traveling the European capitals,” she said. “And of course you would buy a lot of things on the way and send them home.”

Drawing on the “Americans on Vacation” catalogue, I’ve arranged some of the changes since then, an abbreviated chronology that might or might not offer comfort the next time you find yourself in Dallas with a four-hour layover, or in a Parisian hotel with a view of the electrical generator, or nauseated on a Tibetan peak. This, indirectly, is how you got there:

1825: The Erie Canal opens, and soon becomes a venue for tours, some of which climax with a visit to Niagara Falls.

1860: American railroads now run on 30,000 miles of track, up from 3,000 in 1840.

1865: Englishman Thomas Cook, who established the first travel agency 20 years before, opens his first U.S. office, and soon introduces millions to the idea of overseas travel by tour group.

1869: The first transcontinental railroad route is completed.

1877: An essay on Niagara Falls in Harper’s Weekly complains that “what ought be a scene of rest and pleasure, has become . . . a place where all sorts of annoying extortion . . . interfere with one’s enjoyment.”

1888: Kodak introduces its first camera, which it will follow 12 years later with the enormously popular Brownie.

1891: American Express introduces the Traveler’s Cheque.

1893: The first American souvenir postcards are sold at the World’s Columbian Exposition in Chicago.

1902: The American Automobile Assn. is founded.

1906: The New York Times and the New York Tribune inaugurate the first Sunday newspaper travel sections.

1908: The Ford Model T is introduced.

1910: One-third of American manufacturing workers--mostly those in white-collar jobs--now get paid vacation time, a privilege that most of their blue-collar counterparts won’t gain until the end of World War II.

1912: The Idlewild resort in Lake County, Michigan, opens and becomes one of the most popular African-American resorts in the country. It thrives into the 1950s.

1914: The first scheduled air service in the U.S. is inaugurated: “flying boats” between Tampa and St. Petersburg. In the Catskills, Grossinger’s is founded, and goes on to becomes one of the nation’s best-known Jewish resorts.

1930: Boeing Air Transport (later absorbed by United Airlines) hires the first eight stewardesses in America, all registered nurses.

1935: Greyhound buses introduce sight-seeing tours.

1948: The Polaroid Land Camera is unveiled.

1953: In a national survey, 83% of respondents say they now make their vacation trips by automobile.

1955: About this time, air travel surpasses steamship travel as the favorite transportation between North American and Europe.

1962: In his book “The Image,” scholar Daniel J. Boorstin writes that “The modern American tourist now fills his experience with pseudo-events. He has come to expect more strangeness and more familiarity than the world naturally offers.” Boorstin also oberves that “our travels have not, it seems, made us noticeably more cosmopolitan or more understanding of other peoples.”

1963: The Instamatic camera makes its debut.

1971: Federal officials create Amtrak to preserve passenger rail service as private rail companies suffer declines.

1986: Mattel, taking note that 80% of travel agents are women, produces a Barbie Doll travel agent set, complete with pink office furniture and tiny wall posters of global destinations.

1989: The Hamilton, Miller, Hudson & Fayne Travel Corp., aiming to capitalize on the trend toward ever-briefer holidays, tries to sell Detroit residents on the idea of 18-hour Caribbean vacations. For prices beginning at $149.90, the “Day in Paradise” tour leaves Detroit Metropolitan Airport at 7 a.m., returning from the Bahamas at 1 a.m. the next day.

A broadsheet advertising that Bahamian “Day in Paradise” peeks out from one of the exhibit displays. And despite its notable company--the 1870 edition of Mark Twains’ “Innocents Abroad,” for instance, or the wicker seat from the 1930 Ford Tri-Motor passenger plane--co-curator Judith Endelman’s suggested that it might be the most telling artifact of them all.

“I think it says a lot,” she said. “That was sort of the ultimate for me, on this continuum . . . In many ways, the classic sight-seeing tour is dying.”

The Museum of San Diego History (1649 El Prado, Balboa Park , San Diego 92101-1621; 619-232-6203) is open 10 a.m.-4 : 30 p.m. Wednesday through Sunday. Admission for non-membe r s is $3. Exhibit catalogues are available at the museum store for $7.95, or through the Merchandizing Department of the Henry Ford Museum and Greenfield Village, P.O. Box 1970, Dearborn, Mich. 48121.