Except for one detail: nobody could remember where it was. "We have heard it is in the quadrangle," said James Moore, the head. "I just hope it isn't buried under the fish pond."
The school's problems are far from unique. Of 10,000 capsules known to have been buried around the world since the Second World War, 9,000 have been lost, said the International Time Capsule Society (ITCS), a collection of academics who try to advise on how to prepare capsules, what will survive best, and where to put them. The recommendations are: publicise the capsule's existence; do not include anything that will decay easily, and do not bury them - keep them somewhere secure, public and above ground.
But not many people are taking notice. With the millennium upon us, the number of organisations stuffing capsules into foundation stones (aMasonic ritual) and beneath buildings or monuments has rocketed. Future Packaging & Preservation, of Covina, California, has seen its business boom. Janet Reinhold, the owner, says that by the end of the year she will have sold 5,000, including the latest, most popular range - an "individual" capsule, 2ft long, and costing $88 (pounds 55), which people can bury in their back garden. Ms Reinhold said: "It was never this big before. Right now we're doing 13-hour days and I've had to take on extra staff."
The trade is not restricted to the US. Britain's Innovations catalogue lists two and the British Museum reports brisk trade in its pounds 45 brass capsules.
Anyone visiting the museum could also benefit from the advice of one of its staff, Brian Durrans, an ITCS founder. For him, the question of what you put in a capsule - and even what it is for - is almost rhetorical. "It's only illogical to include things which will decay if you think the sole relevant frame of reference for a capsule's contents is what posterity will think. For an individual or a corporation, putting things together for a time capsule makes you reflect about the age you're living in."
Where though did this craze start? Although civilisations have for millennia included artifacts of their time in graves, they were intended for the afterlife. The idea of leaving something for those who would live after us seems comparatively recent.
The Masons' cornerstone deposits were ritualistic, to help buildings last for ever, so they were not time capsules. "Perhaps the Victorian period: there's some interesting stuff under Cleopatra's Needle on the Thames Embankment," said Dr Durrans.
But this time the Government is not taking part in the craze: it is not sponsoring any capsules, and Tony Blair has not contributed to any. Elsewhere though, the eagerness to encapsulate our time is undiminished.
Lane Baumgardner, a machinist from Arkansas, in the US, has spent $20,000 on a complex of four pyramids to contain 20th-century memorabilia. New Zealand is planning a huge "millennium vault".
But perhaps the most "scholarly" time capsule is the "crypt of civilisation" at the home of the ITCS itself, at Oglethorpe University in Atlanta, Georgia. It was sealed in 1940 and will not be opened, it is hoped, until 8113, a point as distant in time from 1940 as was 4233BC - when the Egyptians are thought to have started tracking time - from the date of sealing.
Among the contents of the swimming-pool-sized chamber are 640,000 pages of microfilm, a Donald Duck doll, newsreels of Adolf Hitler, a toaster, the works of Shakespeare, dental floss, and - rather sensibly - a device designed to teach English to the crypt's finders.
THE MOST WANTED MEMENTOES OF THE PAST
In 1991 the International Time Capsule Society prepared a list of the "Most-wanted time capsules". They are:
Bicentennial wagon train capsule
Planned to hold signatures of 22 million Americans and be sealed on 4 July 1976 (the bicentennial) in Valley Forge, Pennsylvania, by president Gerald Ford. But someone stole the capsule from an unattended van in the bicentennial wagon train. It could not be duplicated because the manufacturer, the Reynolds Company, had broken the mould. Neither thief nor capsule has been found.
MIT cyclotron capsule
In 1939 MIT engineers placed a brass capsule beneath an 18-ton magnet used in their particle accelerator, intending to open it in 50 years. The deadline passed but the accelerator (now deactivated) remained, creating the problem for the scientists: how do you extricate a capsule from beneath an 18-ton lid?
The capsules of Corona, California
The city of Corona has misplaced 17 time capsules dating back to the Thirties, despite a concerted effort in 1986 - the city's centenary - to recover them. "We just tore up a lot of concrete around the civic centre", said the chairman of the town's centennial committee.
The `M*A*S*H' time capsule
Buried in January 1983 by cast members of the hit TV comedy show M*A*S*H in a secret ceremony, it contained props and costumes of the show. They secreted it in the 20th Century Fox parking lot in Hollywood, which has since shrunk in size, so the capsule may now rest beneath a
George Washington's cornerstone
In 1793 George Washington, a Mason, performed the Masonic ritual upon the laying of the original cornerstone of the US Capitol building. The Capitol has been expanded and remodelled but the original cornerstone has never been found, and nobody knows if it contains anything.
The Gramophone Company capsule
In 1907 the opera singer Nellie Melba deposited master pressings of recordings by herself and other stars behind the foundation stone of the new Gramophone Company factory in Hayes, Middlesex. During reconstruction in the Sixties the container was removed but, before it could be reburied, someone ran off with it.
Washington territorial centennial capsule
In 1953 Washington state celebrated its territorial centennial by burying a two-ton capsule at the state capitol in Olympia. It was recovered in 1959 but records suggest a supplementary capsule was prepared in 1953 for burial alongside it. The location and contents are unknown.
Blackpool Tower capsule
In Blackpool, Lancashire, a foundation deposit was interred in the late 19th century with customary ceremony. But when a search was organised in the Eighties before building work, remote-sensing equipment could not locate it. Nor could a clairvoyant.
The Lyndon, Vermont, capsule
First mentioned in a 1891 Vermont newspaper, it is an iron box containing proceedings of the town's centennial celebration. It was scheduled to be opened on 4 July 1991, but could not be found. Possibly it was not buried at all: some ceremonies at the time were cancelled due to rain.