Going, going . . . gone] It's magic: If you want to know how to saw someone in half, then hurry off to Sotheby's, says John Windsor

Now you see it, now you don't. I telephoned Mike Heseltine of Sotheby's and said I wanted to write about his massive sale next week of the stage props and conjuring books of the illusionist Will Ayling, who died last year. 'Does Ayling's own book, The Art of Illusion (lot 1059), tell you how to do the Floating Princess trick?' I asked.

'It does,' he said.

'Good,' said I, 'I've always wanted to tell people how to do that.'

I thought I heard a gasp. Then silence. If I intended to reveal how tricks are done, said Mr Heseltine, a confidant of the Magic Circle's most dextrous luminaries and the founder, 14 years ago, of magic auctions, then he could not co-operate. 'I'm not going to do anything which will spoil the enjoyment of performers or audience,' he said.

It was enough to raise the hackles of any self-respecting defender of freedom of information. How could secrets sold at public auction be real secrets?

By the time I met Mr Heseltine at Sotheby's, I had visited London University's Senate House Library, gained access to a copy of The Art of Illusion and avidly photocopied text and diagrams of the Floating Princess levitation trick. Now, I thought, was my chance to offer that vast underclass unable to levitate the means of accomplishing it by guile.

Having admitted my deceit to Mr Heseltine, I made diagrams in the air, indicating to him that I knew all about invisible suspension wires. He replied with an even more theatrical sweep of the hand, indicating the hoop which the stage magician passes around the floating stage assistant from head to toe - apparently unobstructed. He must have noticed my face fall. 'The hoop in lot 1137 is a perfectly ordinary one,' he said.

We looked at each other and laughed.

Well, who said information should be free? Mr Heseltine is not in the business of giving it away. His job is to sell it - in much the same way as newspapermen. 'Famous actor dies,' say the billboards. You must buy the paper to find out who.

The magic of the stage magic business is that although it takes only average persistence to find out how a trick is done, stage magicians still manage to amaze audiences. The exploits of the duo Penn and Teller, who have revealed how tricks are done on Jonathan Ross's Saturday Zoo (Channel 4), berating the magic profession for using 'cheesy tricks to dupe people' are themselves perpetrating an illusion - that their revelations are the result of intrepid sleuthing.

They are not. Anyone prepared to bid an estimated pounds 300- pounds 400 at Sotheby's could walk away with 14 of Ayling's magic know-how books, including both 1968 and 1972 editions of The Art of Illusion, typescripts and Ayling's correspondence with other illustrious members of the fraternity. The Floating Princess props, including an altar platform, two swords and a hoop, are an estimated pounds 200-pounds 300. It is not even necessary to buy them to discover secrets. Simply attend Sotheby's viewing and examine them for nothing.

The biggest secret, I can reveal, is that secrets come in various sizes. What you may think is a big secret may be only a little one. Private gatherings of the Magic Circle are still amazed by new performances of old illusions which demonstrably could not be achieved by traditional methods. For example, Ayling's book cites a dozen different ways of simulating levitation using mechanical devices which you or I could invent. But dextrous use of the hoop can shatter the preconceptions even of professionals.

As Mr Heseltine said: 'It's not just how it's done, it's how well it's done.' The classic sawing-in-half trick, according to Ayling's book, underwent a technical revolution soon after one P T Selbit first performed it in 1920. Selbit enclosed his 'victim' in the box and equipped her with a razor blade (think about it). The real sensation came later the same year when Horace Goldin allowed head and feet to protrude (mark my turn of phrase) and still sawed the box in half. To draw crowds, he arranged for an ambulance and stretcher party to appear near the theatre beforehand.

At the bottom end of the magic market are the kind of schoolkids' boxed conjuring kits that can be bought from toy shops. (Do not scorn them: Ayling, ever receptive to unexpected insights, collected them). At the higher end are limited-edition magic books, sometimes with a locking clasp, sold for a tidy sum to colleagues - such as the two books on 'Exclusive Magical Secrets' published in 1921 by Will Goldston, est pounds 300- pounds 400 at Sotheby's. According to Mr Heseltine: 'Conjurers tend to be so delighted by their own discoveries that they find it hard to keep the secrets from other conjurers.'

In mid-market are retail enterprises such as Supreme Magic of Bideford, Devon, the world's biggest magic retailer. Harry Price's copy of The Art of Illusion bears the fly-leaf sticker of just such a mail order retailer, indicating that Ayling had not limited the edition.

Supreme Magic's 700-page mail order catalogue has 20,000 customers. But the firm does not scatter its secrets with abandon. The catalogue describes only what the audience sees. You have to buy the apparatus to discover the trick. Secrets are revealed in Supreme Magic's 70- page monthly magazine, Magigram, pounds 15 annually, but potential subscribers have to fill in a questionnaire which is scrutinised by the firm's magical adviser, Ian Adair. As a result, circulation is restricted to 9,000, a fraction of Britain's 20,000-30,000 magic enthusiasts, of whom perhaps 500-600 are professionals.

By tradition, a magician's most coveted tricks are passed down to his stage apprentices or family. But Ayling's son, Tony, told me that none of his father's tricks had been withheld from Sotheby's. He said: 'If we kept my father's tricks they would just be stored away and forgotten. When a magician bids for a trick, it is because he really wants it and will present it properly. That is what I want.'

During his 60-year career, Will Ayling, a past president of the British ring of the International Brotherhood of Magicians developed a reputation for presentation - music, costume changes, atmosphere - and for producing cockerels where others could manage only doves.

Budding magicians seeking secrets will go for lots such as 1076: 32 books by Will Goldston dating from 1903, est pounds 200-pounds 300, or lot 1077: two limited-edition books by Robert Harbin, including pencil diagrams for sawing-in-half, with the same estimate. But even the 22 books by Jimmy Findlay, est pounds 1,000-pounds 1,500 (lot 1071), have not been valued for their secrets, Mr Heseltine said. Seasoned performers regard the entire auction as stage history. It is expected to raise more than pounds 20,000.

As I left Sotheby's I saw the most familiar of all illusions. The sun was descending the sky. Spoilsports of the ilk of Penn and Teller have suggested it is not the sun which moves, but the Earth. I have no intention of taking sides. Whoever created the trick might send me a thunderbolt.

Sotheby's auction: Thursday, 2pm (071-493 8080).

Supreme Magic (0237 479266).

(Photographs omitted)