18th-century bone telescopes discovered

Scientists have unearthed five bone-made instruments dating to the 18th century which they say are finely crafted telescopes that may have been used to gaze at objects on land or sea.

Ranging in length from roughly three to five inches, the telescopes -- discovered in Amsterdam, the Netherlands -- were made using cattle metatarsal bone.

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 centre for trade, one that attracted talented craftsmen.

"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.

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.

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, the researchers said.

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, said the researchers who detailed their study in the Journal of Archaeology in the Low Countries.

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.

Rijkelijkhuizen said while she was looking at organic artifacts found in Amsterdam, she came across bone artifacts that would later turn out to be telescopes.

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.

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, the researchers said.