If you can judge a society by its musical instruments (and in fact you can), ours is an age interested in power and brilliance, an age which preaches democracy and enforces conformity. In contrast, the 18th and early 19th centuries were dedicated to subtlety, balance, fine oraments and delicate nuances. The world of two centuries ago was smaller than ours, a society of carefully preserved social distinctions, but also one with more room for individuality.

The special sound of that vanished world can be heard in Washington as in few other cities, because the Smithsonian has one of the world's best collections of playable early pianos and they are heard fairly often in performance. But early pianos are also being heard outside the sheltered museum environment. On July 23, for example, at the University of Maryland International Piano Festival, Evelyn Garvey will give a lecture-recital on "The Sound of Keyboard Music in the 18th Century," using a replica of Mozart's piano.

Listening to the music of the time played on the pianos of the time, it is easy to hear how the world has changed since the American Revolution was followed by the Industrial Revolution. It's all there in the sound of the old pianos.

A good piano today is still largely a hand-crafted work of art, and pianists attach great importance to the differences among varied examples of a particular model. But compared to the instruments made in Beethoven's lifetime, when the piano was still fairly new and rapidly developing, the modern piano is much more standardized; you know approximately what to expect when you sit down to play on one, whether it was made in America, Germany or Japan.

In contrast, a Mozart-era piano made in England (where it was called a "piano-forte") was strinkingly different from one made in Vienna and called a "fortepiano." Look for the pedals on an 18th-century piano, and they may be attached to the legs, so that a player has to do a two-way stretch to reach them. Or they may be levers, suspended under the keyboard and operated by the knees. Some pianos have little knobs, not unlike the stops on an organ or harpsichord, which are adjusted to produce a particular kind of sound, or wedges that can be manipulated to make the notes sound on one or two strings, rather than the standard three, for a more-delicate effect.

On a modern piano, the tone is homogeneous from top to bottom, while on an old piano, each of the five octaves tends to have a distinctive voice of its own -- giving the texture more clarity and sharper cotrasts, and making the interactions of treble and bass sound something like a duet. The notes on an old piano tend to fade more rapidly, to the joy of oboists and violinists, who don't have to work so hard to be heard when they are playing with the piano in chamber music.

Compared to the modern concert grand behemoth, an old piano is tiny -- two octaves less in its range and less powerful of voice. The fortepiano was designed to be played primarily in people's homes or in the palaces of the nobility, and it did not have to cope with the acoustics of the massive concert halls that were built when ticket sales became the central fact of musical life. The modern concert grand is designed to reach the most distant seats in halls that will hold thousands. Playing one in the average living room of the average American home involves a delicate use of power, like riding a motorcycle on a bicycle path.

The piano was smaller, too, because people were smaller. At the Smithsonian, one of the instruments is a Dulcken piano from the mid-1790s. A modern replica of the same piano has been built by the husband-and-wife team of Thomas and Barbara Wolf, who have restored several of the Smithsonian's old pianos. The Wolf replica is identical to the original in almost every detail, but its keyboard is two inches higher above the floor, because the old piano (which has knee-operated levers rather than pedals) is uncomfortably low for most modern players.

Finally, the fortepiano is smaller in price. A fortepiano hand-crafted by the Wolfs and modeled on an old instrument costs about $13,000 -- approximately one-half as one-quarter the price of a good, new concert grand, depending on brand name and model. The price, as well as the more domestic dimensions of its sound, may explain why some people are beginning to order fortepianos for their homes.

The changes in musical instruments have been also been drastic in terms of pitch -- which was much less standardized even in the 19th century than it is today, when it is still not really standard. The current theory is that the A below middle C should be tuned to 440 cycles per second, and that is what they try to maintain in Washington, a city very conscious of standards. But in Boston, it is 444, and in Vienna it is even higher, as some sharp-eared Washingtonians have noted during visits here of orchestras from those cities.

Among 18th-century purists, a convention is gaining acceptance (based on experience with instruments of the period) that the most comfortable compromise is to tune A to 415, almost a half-tone below the modern standard. This may help to explain why sopranos today, using standard pitch, feel uncomfortable with the top notes in Beethoven's Ninth Symphony.But the evidence indicates that A might be have been played, in various places, at anywhere from about 398 to 447.

The suspoicion has been growing for some time that when a modern orchestra plays Bach, Mozart or Haydn, it is likely to produce sounds that those composers never heard or imagined.This had led to various compromises, including reduced orchestras and sometimes the introduction of a harpsichord, which may or may not be heard in a large, modern concert hall -- but if the violins have wire strings and if they are playing at modern concert pitch, the orchestra is still producing sounds unimagined by the composer. Now, the purist trend is moving onward to include Beethoven and Schubert -- with Chopin and Schumann just around the corner.

The time may be coming when three of four instruments will be needed for a single piano recital in the Kennedy Center Concert Hall -- perhaps a Duicken for Mozart and Haydn, a Broadwood for Beethoven, a Pleyel for Chopin or Debussy and a Steinway for Bartok and Rachmaninov.