After the telescope became known in 1608–1609, a number of people in widely separate locations claimed that they had such a device long before the announcement came from The Hague; in the summer of 1608, no one had a telescope, in the summer of 1609, everyone had one. For a number of years Rolf Willach tested early spectacle lenses in museums and private collections, and now he reports on this study, which gives an entirely new explanation of the invention of the telescope and solves the conundrum mentioned above. The book’s foreword is written by Albert van Helden, author of The Invention of the Telescope (Transactions of the American Philosophical Society volume 67, part 4, 1977).