Note 8 — Chapter X

The principle upon which the telescope is based appears to have been known theoretically for a long time previous to this. The monk Roger Bacon, who lived in the thirteenth century, describes it very clearly; and several writers of the sixteenth century have also dealt with the idea. Even Lippershey's claims to a practical solution of the question were hotly contested at the time by two of his own countrymen, i.e. a certain Jacob Metius, and another spectacle-maker of Middleburgh, named Jansen.