Wednesday, 23 August 2017

The Prototype

In 1591 the book Pantometria by Leonard Digges (1515-1559) was published posthumously with an introduction written by his son Thomas Digges. In the introduction mention is made of a proportional glass which can be used to view distant objects but without giving much detail.  Fortunately a decription is given in Inventions or Devises by William Bourne published in 1578. In the book's 110th entry a device is described consisting of a large curved mirror into which one peers and a lens. Bourne commented that the device worked but had a small field of view.  As Leonard Digges died in 1559 we can be certain that he invented his proportional glass before then, possibly as early as 1540. My prototype Digges-Bourne telescope uses a 50mm plano convex lens, two carboard mailing tubes recovered from a rubbish bin and a cosmetic mirror. It is about a meter long and I have photographed it next to a "Tudor LP" for scale.

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