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."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.