"On Time," the new, permanent exhibition unveiled last month at the National Museum of American History, is a case of false advertising (actually, in some ways, it's a case of advertising pure and simple, but we'll get to that later).

It would be more accurate if this Timex-funded exhibit on the history, use and measurement of time in America were called "On the Clock," seeing as how the bulk of exhibition space is devoted to the nearly 200 antique timepieces -- sundials, tower clocks, wall clocks, pocket watches, wristwatches and sundry other varieties of chronometer -- that are on display. Come to think of it, the expression "on the clock" (evocative enough of wage slavery to strike terror into the heart of any working man or woman) is not much better than the original "On Time," which sounds so nice and punctual . . . not to mention philosophical.

And that's the main problem with this show. Its teasing title hints that it might actually delve into such weighty issues as the nature and structure of time itself, but it pretty much restricts its discussion of time to the conventional notion of something stretching behind and in front of us like a road: an invisible ribbon whose unspooling is measured by such milestones as last year, two days ago, yesterday, a minute from now, next summer, when I'm dead and buried.

Einstein's theory of relativity, for instance, is given short shrift. The hypothesis -- from which Einstein deduced, among other things, that the hands of a clock (and hence the perception of time itself) would move slower on a train whose speed approaches the speed of light than would the hands of a stationary clock -- is dispensed with in a single display case. Below a photograph of the maestro sits a small mirror apparatus from the 1920s used to measure the speed of light.

No mention is even made of the current debate among physicists as to whether time necessarily has to move in one direction at all (i.e., forward). And don't even get me started about tachyons, those theoretical subatomic particles that move faster than the speed of light, leading to speculation that (assuming tachyons even exist) one might possibly beam signals with them to one's own past.

But that is neither here nor there and the subject for an exhibition more wonky and less populist than this.

What this exhibition does, and does well, is one thing. It maps out the evolution of the clock, a machine whose name derives from the Middle English word for "bell" in recognition of the fact that its original function was not to tell you what what time it was but to merely mark the passage of the day. In fact, clock dials (faces, as we call them) did not appear until the early 1400s.

In 18th century America, few homes had clocks. By the beginning of the 19th century, however, they had begun moving off church steeples into the homes of a few of the wealthiest people in the form of tall, wooden case (or grandfather) clocks. Eventually, as the size and price came down, the personal timepiece became more prevalent -- in the form of pocket watches worn on the chest or (in the case of women) around the neck or waist. As a result of its role as a status symbol, the pocket watch was often accompanied by elaborate fobs, or ornamental chains, not to mention the ostentatious flourishes with which the proud owners consulted their prized and notoriously inaccurate possessions.

Throughout the exhibit, we encounter a heap of time trivia. We learn that: the division of the day into 12 segments was an ancient Egyptian and Babylonian convention; that in Revolutionary France the day was parceled into 10 hours of 100 minutes each; that in 1818 the first printed schedule of packet ship service between New York and Liverpool was issued by the Black Ball Co.; that in 1853, a collision between two trains outside Pawtucket, R.I., drove home the need for more accurate timekeeping; that the adoption of standard time zones came 30 years later; and that in 1967, by international agreement, a second was defined as the amount of time it takes an atom of cesium 133 to vibrate 9,192,631,770 times when subjected to electromagnetic waves.

This was considerably more accurate, of course, than the definition adopted in the early 1800s, when the fundamental unit of time was defined as 1/86,400 of a mean solar day. Exactly what a "mean solar day" is -- and I don't think it's surfer lingo for peak tanning weather -- "On Time" never tells us.

Another thing "On Time" doesn't tell us is exactly, or even inexactly, how clocks work. In an exhibition devoted to the clock and its many mechanical and electric manifestations, it seems odd that no explanation is given about the construction and working of weight, spring or quartz-driven timepieces. I don't think I'm alone in wanting to look behind the face of the clock and see what makes it -- pardon the expression -- tick.

Some display space is given over to a discussion of our growing modern obsession with time and the idea that we don't have enough of it, or the illusion that we can create more of it by dividing seconds into nanoseconds. There are Palm Pilots, household calendars chockablock with appointments and obligations, photos of graveyard-shift workers toiling in the middle of the night. There's a neon sign advertising a copy business with round-the-clock hours, an old refrigerator that supposedly symbolizes the timesaving appliances of the 20th century. There's a cocktail shaker representing happy hour and a campy old film clip comparing a woman transfering eggs into a storage container the one-handed (i.e., "slow") way with the two-handed (i.e., "efficient") way.

In the end these artifacts, which amuse but do not educate, feel like padding to a thin show anyway.

At the end of the permanent installation is something called the Time Zone, a gallery which will be dedicated to changing exhibitions. Not coincidentally, its current offering is on the history of the Mickey Mouse watch, an early example of cross-promotional marketing synergy between Walt Disney and the Ingersoll-Waterbury watch company (now Timex) that proved hugely successful upon its debut at the 1933 Chicago World's Fair.

Oddly enough, the exhibit is also accompanied by a tape loop of the wonderful "Steamboat Willie," the 1928 black-and-white cartoon that introduced the animated rodent to the world. Mickey, of course, would go on to international celebrity, but his appearance in an exhibition ostensibly "On Time" seems less a result of the fact that "Willie" was the first fully sound-synchronized cartoon than the fact that his popularity helped to move a heck of a lot of watches.

ON TIME -- On permanent view at the National Museum of American History, 14th Street and Constitution Avenue NW (Metro: Smithsonian). 202/357-2700 (TDD: 357-1729). Web site: www.si.edu/nmah. Open 10 to 5:30 daily. Free.