It is one of the epic confrontations in Dickens's novels when, in Hard Times, the circus man, Mr Sleary, faces the stony-faced Mr Gradgrind and lisps this speech:

"Don't be cross with uth poor vagabondth. People mutht be amuthed. They can't be alwayth a learning, nor yet they can't be alwayth a working, they ain't made for it. You mutht have uth, Thquire. Do the withe thing and the kind thing too, and make the betht of uth; not the wurtht!"

A hundred and fifty years later, people still must be "amuthed". They may spend their days in offices and shops and fitted kitchens, but it is made easier by the knowledge that there are still people like Mr Sleary, who are prepared to pitch camp on rough ground and put on a show. As John Mohan says of his traditional fun-fair: "It's a wee bit like rock 'n' roll - it was dead come the Beatles but it still seems to be there yet."

It all started, for the Mohans, more than 100 years ago, when Big Ned Mohan was almost kicked to death by a horse in his blacksmith's forge, and was looking for a career change. He bought a shooting gallery, and later added a peep show to his list of attractions. Don't get the wrong idea - you peeped at four 3D pictures of the Western Front.

It was really when he bought his first set of swinging boats, in 1938, however, that his fate, and that of his family, was sealed. As his grandson says: "I'm a swingboat man. We're not into automatics. You won't see any slot machines here. What we do is supply family entertainment."

John Mohan has a view of his "swingboats" out of the prettily-curtained windows of his caravan, which has just drawn into Killybegs, as part of its summer circuit of Donegal. Yellow, red and blue, they are flying gondolas, romantically made to be pulled into the air by two equal forces

"They're the best set in the country - the best set in Britain or Europe. I'm not just saying that because they're our swingboats. They're made by Thomas of England, and the ironwork was all stamped, a bit like a Rolls-Royce. They're the Rolls-Royce of swingboats!

"If they were invented now, you'd not be allowed," he adds. "They'd say, `These bloody things is dangerous.' But those were the days when, if you came down off the swingboats, it was part of your night's entertainment. Part of the parish's night's entertainment!"

John's father, Sonny, died painting a swingboat. He was born - in a horse-drawn wagon on the fair green in Donegal Town - lived, and died in the trade. "He was painting a candyfloss and a blue boat as well," says John's wife, Vera.

That was in 1988, and by then, John had married and had the first three of his four children. He was fully ensnared by the business, though of course, as a younger man, he had dreamed of escape from the shadow of the swingboats: "I fancied the Foreign Legion no end of times."

The fun-fair had been his whole life and that of all of his relations - he even has an uncle called "Paddy the swing": "Practically every fun-fair in the north of Ireland is a Mohan derivative," he says proudly. "Bells, Herons, McGurks, Grahams, they're all cousins of mine - all Big Ned Mohan descended."

The names tell tales on the mixed history of the region; two of John Mohan's aunts married Protestants and it was what saved them when the Troubles broke out. The Mohans with the Protestant names did the Protestant towns.

While the family tradition pushed John into the business, however, at least he wasn't forced into it by illiteracy, as some patchily educated funfair people are. Moving from school to school was traumatic, but he tries to minimise it: "It was everybody's first day at school - every fortnight."

Nowadays the Mohans spend the winter working on the equipment and don't start touring "lock, stock and barrel" until the end of May so that the three school-going children can stay at school in Whitecross, Co Armagh. When asked will any of them go into the business he says: "I'd like to think they'd have more sense", but adds that some of them probably will: "Francine (16), maybe, or Edward (20)." His reluctance is not convincing - but still, there are reasons for it. "Like most men in the business, I have a bad back and a gammy ticker and arthritis. I'm deaf and noise damage prohibits the operation. The doctor says, `It's you and them damn generators'."

Amazingly enough, Mr Gradgrind's prejudice against travelling "showmen" is still alive and well, too: "Gypsies, tramps, knackers. . . I've had them shouted at me more times than you can shake a stick at."

What makes it all bearable, is that, as Vera says, "People knows us." The Mohans feel part of the communities they visit, mostly in Donegal, and almost always north of a line from Dundalk to Belmullet. Which was what made it all the more difficult when the fun-fair was denounced from the pulpit recently in Rathmullan for having suggestive pictures on its "Miami", which sketches a circle in the air with its line of screaming riders.

The "Miami" has, says John, succeeded the chair-o-planes of the 1930s and the dodgems of the 1940s as "top dog": "If you don't have a Miami, noone wants to talk to you." His Miami represents the investment of a lifetime and he was waiting 18 months for Matt Pennycott, "the best airbrush artist in Britain", to paint it.

"I wanted it to be called `Cuchulainn'. But Matt says to me, `Who's Cuchulainn? Would he be like Robin Hood?' I realised there was no point going into it - the best you'll get is a Viking. So we looked at a few motorbike pictures and pop art in his studio. But I had one stipulation: `If you're putting women in them, put clothes on them'. The manufacturer rang me and said, `He's putting women on it and there's not much clothes on them'." John kept his distance out of deference to "the artistic temperament" and his Miami boasts three pneumatic maidens posed with their Harley-Davidsons, the faces of ZZ Top, and the legend "Live to Ride". In Rathmullan, the radio was hopping with complaints, and at one point John obliged by veiling the ladies with three dust sheets.

He'd been invited to Dublin and west Belfast and Tramore with his Miami, he explains, but no, he'd felt that Rathmullan was entitled to "Live to Ride" like the rest of them. In the end, his defence was this: "I'm sorry to upset you - but it's art. I asked this woman did she ever look at the roof of the Sistine Chapel? Everyone's naked from Adam down."

But they've left all that down the road. By now, the machines have got the caravan shuddering again in Killybegs, and John's wife and children, shadowed by eight-year-old Vicki, are manning the dodgems, the "Old Fashion Sweet Bar", the swingboats. A line has formed at the Miami and John Mohan is itching to get at the controls, with his cry: "Are you ready to scream?"

Despite the downsides of the life, he is what he calls himself, a "Showman", and he looks around the field of ill-assorted children, from dummy-droolers to spotty teenagers, with satisfaction: "You see the faces going around in the dodgems and there are no bad ones." He qualifies: "The good ones outweigh the bad ones."