Alive today, he confided, he'd write ukulele concertos with Peterson, this engaging young Hawaiian (he's also a slack-key guitarist), in mind as the soloist.

Yes, Mozart has always been like that. So, for example, he wrote his Clarinet Concerto specifically to be played by his accomplished friend and fellow freemason Anton Stadler. He wrote his Horn Concertos to be played by Viennese virtuoso Ignaz Leutgeb.

Some of us, in our ignorance, may think the ukulele a rather silly instrument, a tool of trade twanged by singing comedians of the olden days and now played around campfires by grey nomads working their way through Slim Dusty's insufferable greatest hits.

But this columnist's ukulele-ignorance was dispelled at last by just 40 minutes of listening to Peterson playing and talking about the instrument. Peterson is about to perform at the National Folk Festival.

This columnist left the room a ukulele convert but of course Peterson's 12 students, already with a degree of proficiency, were converts long before the all-day workshop. They could play, too. At one point their teacher had them all playing together in concert a hypnotically regular and lovely background melody (''Guys, you could play this all day,'' Peterson enthused) and then, above it all, he added his own solo contribution full of virtuosic sallies and visits to musical styles from lots of lands. This columnist's ears, and Mozart's too, twitched as we thought we picked up fragments of flamenco and of swing and noticed how the ukulele can be tender, moody and wistful in ways that George Formby (the ukulele-wielding comic of yesteryear) never captured while accompanying his ribald songs about window-cleaners spying on honeymoon couples.

As we listened together, Mozart, with his trained, sensitive ear, swore he could hear the sounds of the guitar, the lute, the mandolin, all issuing from the odd-looking thing Peterson was playing.

''Finding a connection with a culture through its music, that's one of the big joys that I find in music,'' Peterson mused just after his solo.

''I find that really fascinating. In Hawaii we have a melting pot of different cultures just like you have in Australia. We have the full heritage of Hawaiian music, that goes back centuries, and then we have influences of the Japanese, Chinese, Portuguese, Puerto Ricans - so many types of influence coming in. This is a very fascinating mixture.''

Hawaii was once blessed, he explained, with a monarchy that included some amazingly well-travelled figures, including a king who was the first king of any country to circle the entire world and who came home with a treasure trove of concepts and ideas. Travelling members of the monarchy brought back to Hawaii ''all this classical music'' they'd heard and that, too, was tossed into Hawaii's musical melting pot.

Not that Peterson (wearing a Hawaiian shirt but a disappointingly tasteful one that seemed to feature designs of grey waves beating on a grey beach on Hawaii's one day of the year of grey weather) spent much of the session showing off. Mozart and I wished he'd show off more. But no, he was mostly engaged in showing his students the nuts and bolts of how to produce the ukulele's repertoire of effects. For when you know how, you can make the ukulele sing, trill and shimmer. You can even, he showed the class to much amusement, have it make ping! and plunk! noises that imitate a tennis ball being struck by a racquet.

''It's had quite an interesting history,'' Peterson explained as he packed his nondescript-looking ukulele away for the workshop's lunch-break.

''It came from the Portuguese, came into the Hawaiian islands with some of the people who came aboard fishing boats. It actually evolved out of an instrument called the braguinha, which is an instrument from Portugal. The Portuguese colonised many parts of the world and if you go to Brazil, there's a strong Portuguese influence … [and] another version of the braguinha played there.

''But in Hawaii [he is from idyllic Maui] it took on a little bit of a different form, using steel strings. Then at one point it started using gut strings, but now we have nylon strings, which give it a sort of a warm sound, not quite as bright … it's a bit like a classical guitar, with that sort of warmth giving it a lot of beauty that you hear in Hawaiian music, some of the music of the islands. And, after all, it came from a European tradition where there was already advanced and evolved string playing. So it comes from a family of versatile instruments, through the guitar, the lute, the mandolin.''

''Told you so!'' Mozart whispered triumphantly in my ear.

The National Folk Festival runs from Thursday, April 17 until Monday, April 21 at EPIC. Jeff Peterson's performances include, on Friday at 11.40am in the Budawang, a concert with Riley Lee, master of the shakuhachi.