A book of 10th-century psalms recovered from St. Catherine’s Monastery on Egypt's Sinai Peninsula is an impressive artifact in itself. But the scientists studying this text at the U.S. Department of Energy's SLAC National Accelerator Laboratory at Stanford University were less interested in the surface text than in what was hidden beneath it. As Gizmodo reports, the researchers were able to identify the remains of an ancient Greek medical text on the parchment using high-powered x-rays.

Unlike the Large Hadron Collider in Switzerland, the Stanford Synchrotron Radiation Lightsource (SSRL) used by the scientists is a much simpler and more common type of particle accelerator. In the SSRL, electrons accelerate to just below the speed of light while tracing a many-sided polygon. Using magnets to manipulate the electrons' path, the researchers can produce x-ray beams powerful enough to reveal the hidden histories of ancient documents.

Mike Toth, R.B. Toth Associates, Flickr // CC BY-NC-SA 2.0

In the case of the 10th-century psalms, the team discovered that the same pages had held an entirely different text written five centuries earlier. The writing was a transcription of the words of the prominent Greek physician Galen, who lived from 130 CE to around 210 CE. His words were recorded on the pages in the ancient Syriac language by an unknown writer a few hundred years after Galen's death.

Several centuries after those words were transcribed, the ink was scraped off by someone else to make room for the psalms. The original text is no longer visible to the naked eye, but by blasting the parchment with x-rays, the scientists can see where the older writing had once marked the page. You can see it below—it's the writing in green.

University of Manchester, SLAC National Accelerator Laboratory, Flickr // CC BY-NC-SA 2.0

Now that the researchers know the hidden text is there, their next step will be uncovering as many words as possible. They plan to do this by scanning the book in its entirety, a process that will take 10 hours for each of the 26 pages. Once they've been scanned and studied, the digital files will be shared online.

Particle accelerators are just one tool scientists use to decipher messages that were erased centuries ago. Recently, conservationists at the Library of Congress used multispectral imaging, a method that bounces different wavelengths of light off a page, to reveal the pigments of an old Alexander Hamilton letter someone had scrubbed out.

[h/t Gizmodo]