Going beneath the surface

The complete PTM system was contained in one 150-pound box. The high resolution X-ray gear from X-Tek weighed nearly 8 tons. "The Mechanism is about 250 millimeters across, a fairly large object, so we needed high energy beams to penetrate it," says Andrew Ramsey, computer tomography specialist with X-Tek, based in Tring, U.K. "The system for that is a small room."

"It's sort of like an electron microscope: we shine our beam onto a metal target, which produces the X-rays, and we use those to create the image," Ramsey says.

The difference from a medical X-ray isit's all real-time and digital, no film. Each scan of the Mechanism resulted in 1,500 to 3,000 separate images, each 2,000 x 2,000 pixels. A computer converts the image into a digital photo and stores it, and then creates a 3-D volume, which cubes the number of pixels. The X-Tek crew ended with 600GB of data. "We were going out to buy hard disks every other day," Ramsey recalls.

The X-Tek system creates super thin slices of the object, which can be viewed via computer from any direction. It was hoped that the X-rays would let researchers in effect peel away the compressed wheels and dials and get an accurate count of the teeth.

But they suddenly found they could do more: the X-rays exposed writing on surfaces mashed together in the Mechanism, and never before seen.

"I was sitting there, taking a virtual slicing plane and moving it into the volume" of one bronze plate of the Mechanism, Ramsey recalls. "I'm rotating it when I see a letter." The letters, 3 to 4 millimeters high, are punched into the bronze plates. "You have to move the [X-ray] slice slowly through the plate, to piece together the full depth of the letter," Ramsey says. "It's a very painstaking process."

He declines to be specific about what the writing says. "But it was basically an instruction manual on using the mechanism, and what its purpose was," he says.

Despite the panoply of brain and technology power brought to bear on the device, much of what drives all of the participants seems to be something more basic, something common to all human beings: the thrill of discovery.

"I felt a bit like Indiana Jones, actually," Ramsey says.