The longest of the telescopes discovered, about in. (140 mm) long and made of cow metatarsal bone, has two finely crafted parts held together with a screw thread. At far left, a lens of the telescope, next to a device with a hole that functioned as an aperture stop.

Five telescopes made of bone and dating to the 18th century have been discovered in Amsterdam, with two of the scopes found in the equivalent of toilets.

At the time, called the Enlightenment, the telescopes would have been considered luxury items and were likely used to gaze at objects on land or sea, rather than to look at the stars. They were created during a period when Amsterdam was a flourishing center for trade, one that attracted talented craftsmen.

Ranging in length from roughly 3 to 5 inches (80 to 140 millimeters), the telescopes were made using cattle metatarsal bone. "This particular bone of cow, the metatarsal bone, is actually quite straight and round," Marloes Rijkelijkhuizen, of the Amsterdam Archaeological Centre at the University of Amsterdam, told LiveScience."It's a nice shape to make these telescopes from, it's straight and (has a) very round narrow cavity."

Each telescope would have had a pair of lenses — like the system used by Galileo — a convex objective and a concave ocular, to magnify objects. (Two of the telescopes have at least one lens intact.) The longest of the telescopes, which had both lenses intact, is made of two parts put together with a screw thread, and was equipped with a bone insertion that has a small hole and likely functioned as an aperture stop. [Quiz: The World's Greatest Inventions]

This finely crafted telescope, with a lens still intact, was found in a cesspit, a place used as a toilet in the 18th century. How it got there is a mystery. (Image credit: Wiard Krook, Office for Monuments & Archaeology, Amsterdam.)

With a magnification of about 3, the bone telescopes may have been used as opera glasses, held up by their wealthy owners to get a better view of the stage. Another idea is that someone going to sea, perhaps as a ship passenger, toted these with them.

The telescopes were excavated at different times over the past 40 years by the Office for Monuments and Archaeology in Amsterdam. Details of the findings hadn't been published until now, and, in the case of two of them, were unidentified until several years ago when Rijkelijkhuizen, then a master's degree student, started work on her thesis. She was looking at organic artifacts found in Amsterdam when she came across bone artifacts that would later turn out to be telescopes.

"At first I didn't recognize them either," Rijkelijkhuizensaid. Her analysis of the five telescopes is now published in the most recent edition of the Journal of Archaeology in the Low Countries.

Found in a toilet

When Rijkelijkhuizenlooked over the excavation reports she found that two of the telescopes had been discovered in cesspits – the 18th-century equivalent of a toilet. It's not clear where the other three telescopes would have been originally deposited in the 18th century.

"It's a toilet but it is also like a dump for trash," she said. Why luxury items like these would have been put in toilets is a mystery; perhaps they broke and their owners, despite the cost of producing them, threw them away. Another idea is that their owners lost them. [A Gallery of the World's Toilets]

Rijkelijkhuizen said it's not the first time she's uncovered unusual objects in pits like these. "We find all different kinds of objects in a cesspit, like false teeth, and we think 'why?'"

However it happened, it was fortunate for the archaeologists. "Because it was a toilet, and it's a very wet environment, all the objects in it are usually very well preserved," she said.

Ushering in the Enlightenment

The 18th century was a time of great change with new ideas, both scientific and political, being discussed. The telescope, with its ability to let people gaze at the stars, and see objects from a great distance, played a significant role in these changes. It had been invented only a century earlier. [The History of Telescopes]

"The telescope (and later the microscope), were thus two major devices that helped usher in the enlightenment," writes Geoff Andersen, an astronomer and author, in his book"The Telescope: Its History, Technology and Future" (Princeton University Press, 2007).

"Suddenly, anyone could experience things beyond the range of the unaided human senses, and start questioning conventional wisdom about the universe in which we live."

Although these newly discovered bone telescopes were not the most powerful telescopes of their day, for their owners it would have given them the ability to peer out farther into the horizon.