A novel technique can read classical texts once thought too delicate to examine
Philosophy of science
IN 1752 Camillo Paderni, an artist who had been put in charge of the growing pile of antiquities being dug up at Herculaneum, a seaside town near Naples, wrote to a certain Dr Mead, who then wrote to the Royal Society in London reporting that “there were found many volumes of papyrus but turned to a sort of charcoal, and so brittle, that being touched, it fell to ashes. Yet by His Majesty’s orders he made many trials to open them, but all to no purpose; excepting some scraps containing some words.”
The excavation at Herculaneum—which, like nearby Pompeii, was buried in 79AD under ash from Mount Vesuvius—had uncovered a literary time capsule. What came to be called the Villa of the Papyri contained a library of perhaps 2,000 books, the only such collection known to have been preserved from antiquity.
The history of the books is tragic. Many were dumped before anyone realised what they were. Perhaps 1,100 were saved, but early attempts to read these were equally destructive. Paderni simply took a knife to them, and though his contemporary Antonio Piaggio, a conservator from the Vatican, managed to build a rack that suspended them from silken threads, letting them unroll under their own weight for months on end, they still tended to break into pieces. Attempts continued into the 20th century, when Norwegian scientists tried applying a gelatine-based adhesive that shrank when it dried, peeling the scrolls’ layers apart in the process. This still, though, left many scrolls in fragments.Actually reading these scrolls has, however, proved both tricky and destructive—until now. For a paper just published inNature Communications, by Vito Mocella of the Institute for Microelectronics and Microsystems, in Naples, describes a way to decipher them without unrolling them.
Some of these fragments can be read with the naked eye. Others require trickery, such as “multispectral imaging”, a way of increasing contrast by comparing pictures taken under different colours of light. Moreover, the outermost layers of those scrolls examined, and thus the beginnings of the books concerned, have proved too delicate for any technique before Dr Mocella’s to recover. What has been learned is, nevertheless, tantalising.
The library is composed mostly of treatises on the philosophy of Epicurus, a Greek philosopher of the late fourth and early third centuries BC. At least 44 are by a single author: Philodemus, an empiricist, who was a close friend of Calpurnius Piso, Julius Caesar’s father-in-law. Many historians thus believe the villa originally belonged to Piso, though both he and Philodemus had been dead more than a century at the time of the eruption.
The attentions of previous investigators mean that most of the scrolls are now in pieces. Still, over 200 remain untouched, and it is to these that Dr Mocella turned his attention. He used X-rays to probe them—but not any old X-rays. His are generated by the European Synchrotron Radiation Facility (ESRF), in Grenoble, France.
A coherent argument
The way X-rays are used in hospital radiology departments, to show differences in density—as between bones and surrounding tissue—would not work on the scrolls. The inks of antiquity were made of soot: nearly pure carbon, the same stuff that the charred papyri now consist of. A normal X-ray image would thus look blank. Instead, Dr Mocella employs phase-contrast imaging, a technique which works because the ink in the scrolls has not been absorbed into the papyrus, but instead sits on top of it. That means an X-ray takes a tiny bit longer to traverse a part of a papyrus that has ink on it than one that does not.
This difference is detectable, however, only if the X-ray beam is coherent—meaning that the waves it is made up of start off in step with one another. When such a beam has passed through a scroll, its waves will no longer be in step. Some will have been slowed down only by the papyrus while others have been slowed by both papyrus and ink. The former and the latter will interfere with one another, reinforcing each other in some places and cancelling each other out in others, thus producing a pattern that indicates just where the X-rays were delayed by ink.
X-rays from a normal source are not coherent, but those from the ESRF, an instrument Dr Mocella knows well because he used it for his doctoral work, are. He therefore begged some time on it (it is more usually devoted to things like materials science and protein crystallography) and tried it out on two scrolls.
He and his colleagues rotated each scroll in the ESRF’s beam and stitched the resulting interference patterns together using a computer. They ended up with three-dimensional scans of the scrolls, inside which the individual letters can be read.
Their work is still in its early stages, and the team has so far managed to decipher only a few phrases. But Dr Mocella believes the software used to unpick the diffraction patterns can be improved, and that probing scrolls using X-rays of different wavelengths will increase the amount of contrast in the images.
There is much at stake. Epicurus wrote a 37-volume treatise on empiricism called On Nature, perhaps the most comprehensive basis in classical times for the modern notion of learning through experimentation. Fragments of ten of the volumes have been found among the villa’s treasures, so there is a good chance that more lie among the unexamined scrolls.
For Dirk Obbink, a professor of classics at Oxford University, the promise lies in at last being able to look at the opening words of a classical book: dedications and forewords with rich and never-before-seen historical content. These would probably confirm, for example, whether the villa really was Piso’s. As Dr Obbink puts it, “I’m planning on living long enough to read one of those with the new technology. Last week, I wasn’t.”