Invisible Airs, Contraptions, Bristol, UK

bnr#55 => Invisible Airs, Contraptions, Bristol, UK

Dolland Telescope

Object: 11

Dolland Telescope

Date of origin: 1757
Author/inventor/context: John Dolland, Peter Dolland

Before the mid-18th Century, Telescopes were very long to overcome the non-uniform refractive properties of the lense glass. This made the telescopes difficult to move and limited their use. The Dolland telescope of 1757 overcame the problem of chromatic aberration, eventually introducing the triple objective, a combination of two convex lenses of crown glass with a concave flint lens between them. Dolland's invention created the market in portable telescopes, the spy satellite of the 18th Century. It radicalised warfare and was fundamental to the visual telegraphs created in post revolutionary France. This telegraph changed the speed of message delivery from 100 miles a day to 400 miles an hour, paving the way for the electric telegraph.

Graham Harwood