Narrator:Listen to part of a lecture in an art history class.
Professor:Now in Europe in the Middle Ages before the invention of printing and the printing press, all books, all manual scripts were hand-made.
And the material typically used for the pages was parchment, which is animal skin that stretched and dried under tension, so it become s really fat and can be written on.
During the 1400s, when printing was being developed, paper became the predominant material for books in Europe, but prior to that, it was parchment.
在 15 世纪，印刷术得到发展的时期，纸张变成欧洲主要制作书籍的材料，但是在那之前，是羊皮纸。
Parchment is durable, much more so than paper, and it could be reused which came in handy since it was a costly material and in short supply.
So it wasn't uncommon for the scribes or monks who produce the manual scripts.
Ah, remember before printing books were made mainly in monasteries.
Well, the scribes often recycled the parchment that'd been used for earlier manual scripts.
They simply erased the ink off the parchment and wrote something new in its place a manual script page that was written on, erased and then used again is called a palimpsest.
Palimpsests were created, well, we know about two methods that were used for removing ink from parchment.
In the late Middle Ages, it was customary to scrape away the surface of the parchment with an abrasive, which completely wiped out any writing that was there.
But earlier in the Middle Ages, the original ink was usually removed by washing the used parchment with milk.
That removed the ink.
But with the passing of time, the original writing might reappear.
In fact, it might reappear to the extent that scholars could make out an even decipher, the original text.
Perhaps, the most famous example is the Archimedes' palimpsest.
Archimedes lived in Greece around 200 BCE, and as you probably know, he's considered one of the greatest Mathematicians who ever lived, even though , many of his writings had been lost , including what many now think to be his most important work called The Method.
阿基米德在大约公元前 200 年前居住与希腊，你们可能知道，他被看做是亘古以来最出色的数学家之一，即便他多数的手稿都已经丢失，包括我们现在认为的他最重要的成就，称之为方法论。
But in 1998, a book of prayers from the Middle Ages sold in an art auction for a lot of money, more money than anyone would pay for a damaged book from the 12th century. Beautiful or not, why?
但是在 1998 年的一个艺术拍卖会上，一本中世纪的祈祷书被高价拍卖，比任何一本 12 世纪的受损书籍的价格都要高。很神奇吧，为什么呢？
It had been discovered that the book was a palimpsest, and beneath the surface writing on the manual script laid, guess what?
Mathematical theorems and diagrams from Archimedes.
Archimedes' writings were originally done on papyrus scrolls.
Then in the10th century, a scribe made a copy on parchment of some of his texts and diagrams including, as it turns out the Method.
然后在 10 世纪，一个抄写员将他的附图的文章都抄写在羊皮纸的上面，这就是方法论。
This was extremely fortunate, since later on, the original papyrus scrolls disappeared.
About 200 years later in the 12th century, this parchment manual script became a palimpsest when a scribe used the parchment to make a prayer book.
大约在200 年后的 12 世纪，这个羊皮纸手抄稿变成了一个重写本，因为一个抄写员用这张羊皮纸制作成了祈祷书。
So the pages, the pieces of parchment themselves, had been preserved.
But the Archimedes' text was erased and written over, and no one knew it existed.
It wasn't until 1906 that a scholar came across the prayer book in a library and realized it was a palimpsest, and that the underlying layer of texts could only have come from Archimedes.
直到 1906 年，一位学者来到图书馆偶然看到这本祈祷书，并意识到了这是本重写本，而下面藏匿的内容仅有可能是来自阿基米德。
That was when his work The Method was discovered for the first time.
Um... the palimpsest then went through some more tough times, but eventually it ended up in an art auction where was bought and then donated to an art museum in Baltimore, for conservation and study.
To avoid further damage to the manual script, the research team at the art museum has had to be extremely selective in their techniques they used to see the original writing.
They've used ultraviolet light and some other techniques, and if you're interested in that sort of thing, you can learn more about it in an art conservation class.
But actually, it was a physicist who came up with a method that was a breakthrough. He realized that the iron in the ancient ink would display if exposed to a certain X-ray imaging method, and except for small portions of the text that couldn't be deciphered, this technique's been very helpful in seeing Archimedes 'texts and drawings through the medieval over writing.
但是实际上， 是一位物理学家想出的方法有了突破。他意识到古墨水中的铁会在一定的 X 光影像处理方法中显露出来，除了一小部分的内容还没有被破解，这项技术通过中世纪的重写本对我们看阿基米德的文章和图解及其大的有帮助。