Many chaps occasionally fancy themselves as inventors, along the lines of Tintin's Professor Calculus or the Famous Five's Uncle Question. Staring into the distance, we muse on electronic gizmos that will make our fortune or perpetual-motion machines to transform the lot of humanity.

Most of our chimeras, thank goodness, stay exactly that. But at the Great British Innovations and Inventions Fair, held at the Barbican the other day, there was a large gathering of boffins and entrepreneurs who had pushed their pipe dreams as far as building a prototype and, in a few cases, even to the production line.

A random sampling of stands produced a rich mix of creative imagination and perhaps excessively high hopes. A chap from Skye, who had previously invented a plastic home for scallops, demonstrated his latest notion - a gadget that induces sleep in infants by mimicking the sound and motion of a motor car. The child's pushchair is randomly jarred and shaken to the accompaniment of a soundtrack. Whether Citroen will be pleased that one of its models has been used to provide the rumbling, the squeaks and the gear changes is a matter for conjecture. Unfortunately, like many prototypes at the exhibition, the device wasn't working very well. "Something wrong with the modulation," its creator tutted. "But the level of interest is amazing."

Nearby, a genial family party were playing the board game they hoped would take the world by storm. "It's called Jagabongo," the inventor told me. "We came up with the name in 1981. Then we had to think of a game to match it."

Elsewhere, a rare female inventor demonstrated "Barney, the Auto-mate Instant Car Passenger - a great idea for lone drivers who don't wish to appear alone". "He comes in an executive-style briefcase," she said mysteriously. "You plug him into the car cigar-lighter to inflate. As soon as you've reached your destination, you flip a switch and five seconds later he's back in the attache case." Each "passenger" will be unique, with different clothing, skin colour and hair.

The relentless flow of inventions - bootees for police dogs so they can walk on broken glass, a plastic trellis to stop your car doors being knocked in car parks, a filing cabinet that fits in a kitchen cupboard, a clip that keeps bait on unbarbed hooks - makes one doubt the old saw that necessity is the mother of invention. For many people, it seems, invention is a necessity pure and simple. Apparently the British Library holds 38 million patents and receives a million more each year. "We've got more inventors per square inch than anywhere else. The bad news is that they're not coming up with viable products," warned Douglas Buchanan of the Institute of Patentees and Inventors. "You might make a better mousetrap than anyone else, but it's no use if you haven't any mice." Indeed so. Us weasels knew that already.

It's nice to hear that Stonehenge has emerged as an example of "fast track" building techniques. Until last week it was believed that the great megalithic structure had taken about 1,600 years to complete - a construction period comparable to that of the still-unfinished British Library. But as a result of a new method of radiocarbon dating, it has emerged that most of Stonehenge was in fact completed in only 300 years - much in the way that new superstores and out-of-town DIY warehouses are flung up in just a month or two these days.

The great stone doughnut of Salisbury Plain presaged modern Britain in other respects. On a bright morning in July 1953, an archaeologist called RJC Atkinson spotted for the first time that one of the big upright stones bore a carving. There's nothing special about that, of course, since most of the rocks have gathered inscriptions in recent centuries; but this was a prehistoric carving of a dagger, dated to about 1500bc. Even then, it seems, the British were keen on graffiti and had a distressing fondness for knives.

Regular readers may remember my sounding off about Buckingham Palace's 45 acres of empty gardens in the heart of London. Well, I still haven't managed to get in, but the other day I did gain admission to the second largest private garden in central London - in the grounds of Lambeth Palace, where Archbishops of Canterbury have been wielding trowels and dipping dibbers since 1190. The archiepiscopal plot was, with wild generosity, opened to the public for a single day as part of the National Gardens Scheme.

It seemed a strange day to choose, so early in the season. Had the Archbish gained some divine dispensation in the meteorological dept? Sadly, no. The Palace of Westminster looked as misty across the river as when it was murkily portrayed by Monet in the 1870s. And there wasn't a great deal to see, around the greensward once stormed by Wat Tyler and strolled by Cranmer. The daffodils were still tightly in bud, and the sweet cicely was sourly lurking below ground. Mrs W and I mooched round, glaring at the twig-like mulberry tree planted, as a sign informed us, "by the Worshipful Company of Fruiterers on the day Terry Waite regained his freedom" and the Oriental garden created by the equally exotic Mrs Rosalind Runcie.

"Last year we picked a day in April and all the daffodils had gorn," explained one of the plummy-voiced grandes dames who care for the garden. "So this year we brought it forward by a month. Now we're too early because of the bad winter and nothing's come through yet." It's a point worth mulling over by anyone planning an early holiday or a premature barbecue. If the sun won't shine on the A of C, what chance have the rest of us?

Different generations go deaf for different reasons. My esteemed pater, Mr Weasel Senior, suffered a degree of hearing loss when his rifle misfired during the Second World War. Mrs W, a product of the baby boom, hardly heard a thing said to her in the Seventies once she had found out how to work a Sony Walkman. The Eighties crowd cannot conduct an ordinary conversation unless it is down a mobile telephone. Me, I've been a bit Mutt and Jeff ever since going to see a group called the New York Dolls in Hull some time in the early Seventies. My God, they were loud. They attracted only a few dozen Humbersiders, but left me with a lasting souvenir in the form of a distant but persistent shushing noise in my left ear.

Now a report in New Scientist reveals that about 44 per cent of rock concert-goers have symptoms of deafness (usually temporary) afterwards. According to French audiologist Christian Meyer-Bisch, people who listen to live music are far more prone to permanent hearing loss than those who prefer discos. After recording Madonna screeching at 117 decibels, M Meyer-Bisch points out that rock concerts have become a "serious public health concern".

Too late, I fear, to be a salutary warning to Pete Townshend, The Who's hawk-nosed arm-flailer. Those most afflicted by this condition (the report concludes) are the performers. I notice that many now wear earplugs while on stage. Poor Pete has been so deafened by his own output that, on the last Who tour, he had to perform on stage in a Plexiglas structure resembling a plastic telephone kiosk. Since then, he's refused point-blank to do any more touring. But that hasn't stopped him inflicting monstrous noise on an only-too-willing audience, as the new stage version of Tommy lately hit the West End to great acclaim.

"Tommy, can you hear me?" Pardon?