It might not look much, but this small disc of metal helped shape science because it was the primary mirror in Sir Isaac Newton's original reflecting telescope.
Made from speculum—an alloy containing tin and copper with some arsenic thrown in—it was a crucial part of the telescopes of the day. And this one just happened to be used by one of the world's most influential scientists to help him understand how the Universe worked. Now housed in the Royal Society, London, this video takes a closer look at how a simple disc of metal helped change science. [YouTube]