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Document number: 6252
Date: 06 Feb 1863
Recipient: TALBOT William Henry Fox
Author: TAIT Peter Guthrie
Collection: British Library, London, Manuscripts - Fox Talbot Collection
Collection number historic: Acc 38757
Last updated: 8th November 2012

6 Greenhill Gardens,
6 / 2 / 63

My dear Sir,

It is easy to show by analytic geometry that the locus of any point in a line of constant length whose ends move in two intersecting lines is an ellipse; but I think you will be pleased with the following geometrical proof.

[diagram] When the circle OAB rolls within another of double size, the points A & B describe diameters OA' & OB' & AB is of constant length; Also any point of the circle’s area, and therefore any point of AB, describes an Ellipse.

Yours very truly
P. Guthrie Tait.

H. F. Talbot Esqre

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