If you’re like me, you hardly write by hand on paper anymore. And when you do, the handwriting looks terrible. Blame our digital devices, I guess. It’s perhaps for this reason that it’s to imagine there was a time when paper was an extremely rare and hard-sought commodity.

Just imagine: to produce enough parchment to make a Bible, the skins of as many as 200 sheep may have been needed. Writing was expensive. One way to save parchment was to write words and sentences in small script in a continuous fashion, with no punctuation. Reading was difficult and open to interpretation, but it saved space.

But another way to save parchment and papyrus was to recycle it. Typically, papyrus scrolls were inscribed on only one side, where the fibers ran horizontally, making it easier to write. The reverse side, which had vertical fibers, was usually left blank. However, during times of scarcity, scribes would make use of this less convenient side for writing documents deemed less important, such as tax receipts and payment reminders.

Recycling parchment pages was not as easy because scribes would use both sides. To create new blank pages, scribes selected books that were no longer used, difficult to understand, or perhaps even prohibited. They then removed the original writing by scraping or washing it away, resulting in what we now refer to as a palimpsest, meaning a “re-scratched” page.

Numerous manuscripts containing these recycled pages have been preserved, and uncovering the original texts beneath the new writing is always fascinating and full of surprises. However, deciphering these underlying texts can be challenging. In some cases, the original text was not thoroughly erased, allowing modern observers to easily see and identify it. Notable examples of such texts include the epics of Homer and the mathematical works of Euclid of Megara.

However, thanks to modern technology, even when the recycling is meticulous, it is possible to recover the original text. More recently, a manuscript once thought to be penned by Claudius Ptolemy, the renowned Egyptian mathematician and astronomer of Greek descent, has been deciphered. The ancient text, dating back to the first century A.D., was overwritten by another scholar in the sixth or seventh century AD.

The new reveal offers unprecedented insight into early astronomical studies and technologies. It’s, in fact, a manual for how to build an intriguing astronomical instrument meant to measure the distance between stars.

Discovery and Deciphering

Hidden within the confines of Bobbio Abbey’s library in northern Italy, this document languished in obscurity for centuries. It wasn’t until 1819 that was discovered by Angelo Mai, a Roman Catholic cardinal and scholar. Ptolemy’s Greek writing was overwritten by Spanish theologian Isidore of Seville’s “Etymologiae”, a work in Latin.

However, after carefully studying several pages, Mai realized this was a palimpsest – a manuscript page or document that has been written on, scraped off, and used again, often visible with remnants of older writing beneath the newer text..

Mai attempted to “clean” the pages using chemical reagents. In the process, he was able to erase some of the Latin writing, partially revealing Greek mathematical texts with scientific diagrams on thirty pages. He couldn’t make much of it though, and his unpublished transcription was later deposited at the Vatican Library.

In 1880, the document resurfaced yet again when it came to the attention of scholar Christian Belger, whose task was even more difficult than Mai’s due to the many dark brown stains left by the chemicals. Nevertheless, Belger was able to copy two more pages from the palimpsest, which was named Fragmentum mathematicum Bobiense.

Over the years, many other scholars contributed to the study of this most intriguing text, some recognizing fragments from parts of Ptolemy’s On the Analemma, a short treatise on geometrical constructions related to the theory of sundials. It was never very readable though, apart from some isolated words and half sentences here and there.

However, the greatest achievements have been achieved more recently starting in the early 2000s. Scientists subjected the palimpsest pages to UV fluorescence and multispectral reflectance imaging to highlight and contrast the different types of texts penned at different times. The idea is that each type of ink reflects different wavelengths of light. What multispectral imaging does is it snaps an image for each wavelength, then all these images are combined in a way that makes the writing you want to see pop up.

These painstaking investigations revealed that the ancient palimpsest indeed contained references to Ptolemy’s previous works. However, the most significant textual discovery has been the discovery of parts of Ptolemy’s treatise on the instrument called Meteoroscope. Because the earliest or last pages of this treatise are missing, there is no title for this scientific document, so researchers at Sorbonne University in Paris and New York University (NYU) have provisionally called it On the Meteoroscope.

Who was Ptolemy and what’s a meteoroscope?

Claudius Ptolemy was a significant Egyptian-Greek astronomer, mathematician, and geographer who lived and worked in Alexandria, Egypt, during the years AD 127 to 141. At the time Egypt was a province part of the Roman Empire. Known for his geocentric model of the universe, which placed the Earth at the center, his work influenced the fields of astronomy and geography for over 1400 years until the heliocentric model of Copernicus gained acceptance.

Ptolemy was the first to use longitudinal and latitudinal lines in his world map, which was part of his 2nd-century treatise, Geography. This concept of a global coordinate system has had a profound impact, laying the foundation for the similar system we utilize today.

Very little is known about Ptolemy’s personal life. It’s suggested he was born in Hermiou, Upper Egypt, but this is based on sources from over a thousand years after his time, making it uncertain. His name suggests he was of Greek descent living in Egypt and possibly had Roman citizenship judging from his first name. It’s believed his teacher was the Greek mathematician and philosopher Theon of Smyrna.

Ptolemy’s most famous work is the Almagest, a comprehensive treatise on the mathematics of the motions of the Sun, Moon, and planets. This work, which detailed a geocentric model using epicycles and deferents to explain planetary movements, remained the authoritative text on astronomy until the Renaissance. Despite its later replacement by heliocentric models proposed by Nicolaus Copernicus, the Almagest reflects Ptolemy’s immense legacy and influence on the mathematical and theoretical understanding of the cosmos.

Ptolemy also wrote on optics, studying light, reflection, and refraction, as well on astrology, linking the positions of celestial bodies with human affairs, a common practice of his time.

Despite his contributions, Ptolemy’s work has been a subject of controversy. Some historians accuse him of falsifying data to fit his theories, a claim that has led to debates about his scientific integrity. American physicist Robert Russel Newton was particularly harsh. He thought Ptolemy was a fraud of the highest degree, going as far as calling him “the most successful fraud in the history of science”. The accusation is that Ptolemy ‘cooked the books’, so that his results matched his preexisting theories. In his 1977 book The Crime of Claudius Ptolemy, Newton wrote:

“This is the story of a scientific crime. … I mean a crime committed by a scientist against fellow scientists and scholars, a betrayal of the ethics and integrity of his profession that has forever deprived mankind of fundamental information about an important area of astronomy and history.”

“[Ptolemy] developed certain astronomical theories and discovered that they were not consistent with observation. Instead of abandoning the theories, he deliberately fabricated observations from the theories so that he could claim that the observations prove the validity of his theories. In every scientific or scholarly setting known, this practice is called fraud, and it is a crime against science and scholarship.”

Technology and ancient texts deciphered

Others defend Ptolemy, arguing that he worked within the limitations of his era’s observational techniques and theoretical frameworks. Whichever part of the aisle you’re at, one can’t deny that Ptolemy was a gifted scientist. You may forgive some of his transgressions once you place him in the proper historical context — this is a scholar who lived 2,000 years ago, let’s not forget.

The meteoroscope is particularly revealing of his genius. This is an advanced armillary instrument (a spherical astrolabe) used by ancient astronomers to measure distances and study the stars. This device, essential for the astronomers of antiquity, consisted of nine metal rings capable of pivoting around each other, enabling the user to conduct precise astronomical calculations. The treatise recently uncovered and deciphered more than 200 years after its discovery contains instructions on how to assemble and use such an instrument.

But how can the researchers be really sure that these writings truly belong to Ptolemy? Since these are fragments stitched together from surviving pages, there is no beginning or end. As such, there are no treatise titles or author names. In the mind of Alexander Jones, a professor at NYU’s Institute for the Study of the Ancient World and co-author of this study, there can be no doubt that this was Ptolemy.

“Unfortunately, we don’t have the first and the last pages, so we don’t have an author name,” Jones told Live Science. “But things started showing up that are very characteristic of Ptolemy’s Greek vocabulary. He has a distinctive style and uses certain phrases and words that either no one else used in all of ancient Greek literature or hardly anybody unless they were influenced by him.”

“Then we found a particular passage where the author is speaking in the first person, saying, ‘I introduced a new terminology for certain angles used in astronomy,'” Jones said. “We also have another book by Ptolemy where he used the same terminology of new names for these angles. That’s our strongest piece of evidence that it is by him.”

The findings appeared in the journal Archive for History of Exact Sciences.