Why should anyone in a hundred or a thousand years' time be remotely interested in our wedding photographs and football programmes? The Ancient Egyptians - time encapsulators par excellence - harboured no such illusions. The objects in Tutankhamen's tomb were not for us, they were for the boy king to use in another, better, life.
We live in more arrogant times, however. Convinced that in the future, people will be enthralled by our Bay City Rollers scarves and old Budweiser cans, we are flocking to buy cheap time capsules on the high street - and more expensive ones by mail order.
There are larger projects, too. Blue Peter's Millennium Dome capsule will be buried at the Dome in digital form, for 50 years, and the United States time capsule monument has room for thousands of personal items. In Fiji, a one-kilometre-long Millennium Wall will house thousands of messages in steel tubes. Britain's Millennium Time Capsule Project is an ambitious plan to house thousands of individual capsules, to be opened in 200 years.
Where did it start, this burning desire to be remembered and recognised in this way? After the Egyptians and the pyramids, more modern versions of the concept were the messages left under foundation stones, often as part of Masonic ritual.
Then in 1940 came what must still be a seminal project: The Crypt of Civilisation was a swimming-pool-sized room filled with hundreds of thousands of objects and letters, ceremonially sealed behind a welded steel door until 8113 (which is supposed to be as far from 1940 as 1940 is from the first recorded historical date.) The Crypt is at Oglethorpe University in Georgia, which is now the headquarters of the International Time Capsule Society.
Unsurprisingly, the longer the capsule is intended to last, the more complicated the preservation arrangements have to be - 50 years might be plastic pop bottle country, but 100 years is not, and beyond that you need expert help.
Let no one be deterred. The making of a time capsule is done only partly for the benefit of the openers. At least as important is the preparatory process of selection and reflection. This is why a time capsule is an excellent project for any community, and particularly a school.
Sue Gill of Engineers of the Imagination, publishers of the excellent and entertaining The Dead Good Time Capsule Book, has worked on numerous time capsule and related events.
"It doesn't have to be dreary, dutiful and worthy," she says. "It's a fantastic opportunity to invite the children to express what it is that gives meaning to their lives, what they might want to say to a child of their own age in the future."
The process is the important part, she says. "It can be creative - a piece of writing, some artwork, music, possibly even something three-dimensional. It's a lovely opportunity for some reflection about values and meanings."
Gill, whose organisation is deeply interested in rites of passage and secular rituals and ceremonies, suggests that filling the capsule should be a significant event. "When we did ours, it took three hours on a Saturday morning. It's that thing about the last sight of the object before it goes in; then the placing, the wrapping, the binding them up. And always there's the poetic question of who will be the next person to see it."
She urges teachers not to be hung up on the techniques of preservation. "You can get highly technical, but at the end of the day you cross your fingers. I'd hate teachers to be daunted by intimidating technology. We all know if you move house sometimes you find things - papers, shoe boxes with things in - that have survived. So don't be too anxious."
In any case, it is not always necessary to go for a very long period. A 25-year time span would give huge pleasure to the children at the time of its sealing, and to those chilren as adults, re-united for another ceremony to open the capsule.
It need not be buried - in fact this is not the best option for preservation. It could be in a wall behind a plaque, or even hanging in full view from a rafter.
But make sure that you record where it is. The International Time Capsule Society will do this for you and undertake to contact the right people when opening time comes. This is important - the ITCS reckons that of the 10,000 or so time capsules actually known to have been buried in the past, 9,000 are lost.
In Gas City, Indiana, the whole community gathered one day to witness the unearthing of a time capsule near to the town hall. They dug up the car park, all the lawns and flowerbeds, and took down the flagpole to peek underneath. The capsule, alas, was never found.
Stainless steel is best. You can use plastic, but not PVC, as it deteriorates and emits an acid gas. Glass and ceramic are fine provided they aren't going to get broken. For a big short-term capsule, you could use a plastic dustbin with a sealed lid. Wood is problematic, but museums have lots of very old wooden artefacts, so it's clearly worth a try.
The site Put your capsule somewhere dry. If it's in a wall, don't expose it to the annual cycle of frost and direct sunlight.
Discovery Time Capsules provide a suggested list with their capsules. Some items are predictable - coins, newspapers, recipes - others aregently amusing, such as "a recipe for beer and a glass from which to drink it". Surveys show that people want to put in laptop computers, CDs and videos, but these won't really last all that long though - videos and audiotapes deteriorate after about 20 years. In any case, don't put in batteries.
Good sense says keep it simple. To keep everything dry, use silica crystals, supplied with good capsules. For writing, remember that pencil lasts longer than ordinary ink, especially if the paper is sprayed with a de-acidifier (get it from a preservation supplier as it's essential for newsprint, which is very acid). Wrap things individually to prevent problems spreading. Black and white photographs last longer than colour. Don't put in anything rusty.
* The International Time Capsule Society in Britain can be contacted by writing to Brian Durrans, The British Museum, Burlington Gardens, London W1X 2EX. E-mail: firstname.lastname@example.org * 'The Dead Good Time Capsule Book', edited by GP Gill, is essential reading, with lots of information and many more contacts. You can order it from Engineers of the Imagination, Welfare State International, Lanternhouse, The Ellers, Ulverston, Cumbria LA12 0AA. pound;6.95 plus pound;1.50 postage. Tel: 01229 581127 E-mail: email@example.comWebsite: www.welfare-state.org * There are two main specialist firms that give advice and supply high-quality stainless steel capsules. Discovery Time Capsules (96 London Road, Marlborough SN8 2QP; tel: 01672 512120; website: www.time-capsules.co.uk) has capsules from pound;250. Preservation Equipment (Diss, Norfolk IP22 2DG; tel: 01379 651527; website: www.preservationequipment.com) has capsules from pound;280. A silver-plated time capsule with copper costs pound;75 inc postage, by mail order from London Emblem, Unit 200,Fareham Reach, 166 Fareham Road, Gosport SO13 0FP. Tel: 01329 227353 * A Present Day Time Capsule from Hope Education, with photocopiable sheets at pound;24.95 plus VAT, is obtainable from Hope Education, Orb Mill, Huddersfield Road Oldham OL4 2ST. Tel: 0161 628 2790. Marks and Spencer's capsule is available in most stores for pound;12. The Science Museum shop has a time capsule, with instructions, for seven-year-olds upwards. pound;19.99.
* To take part in The Millennium Time Capsule Project, write to PO Box 736, Newcastle upon Tyne NE99 1LQ. The Schools Pack costs pound;39 plus pound;2 pamp;p. Website: www.time-capsule.com * The British Museum will be holding a Time Capsule day on Sunday March 26, 2000.