495 of 520
Sorted by:
Instrument type

Signed by Augustine Ryther
Dated 1590; English
Brass; 235 mm in diameter

The altazimuth theodolite has a base socket with a clamping screw, rising to a short plate with two holes where wing-headed screws secure the circular horizontal plate, cut away to form a square inscribed within the circle, while inscribed within the square is a disc with a central hole for the vertical pivot and two threaded holes for securing screws. The outer circle has a scale of degrees 0 to 360, divided to 10, subdivided to 5 and to 1, numbered by 10. The square has four shadow squares, each with scales 0 to 60 to 0, divided to 5, subdivided to 1, numbered by 10, with inner scales 0 to 12 to 0, divided to 3, numbered by 3.

Above the horizontal plate pivots a counterchanged alidade with folding slit and window sights, and attached to the alidade is a circular glazed compass box with a needle and coloured compass rose, with initialled cardinal points and a circular scale 0 to 120, divided to 10, subdivided to 5, to 1 and to 1/2, numbered by 5.

Carried above the alidade by a brass ring surrounding the compass box, is the support for a vertical semicircle, with an inscribed double shadow-square, and above the semicircle an alidade with pinhole and window sights and slit sights. The semicircle pivots in the vertical plane with the alidade, and has a clamping screw, the scales on both sides being read by fiducial edges in the stand. A short plumb-line is missing. Each side of the semicircle has a degree scale 90 to [0] to 90, divided to 10, subdivided to 1, numbered by 10; each side of the double square has scales 0 to 12 to 0 to 12 to 0, divided to 3, subdivided to 1, numbered by 3. The vertical semicircle, etc, can readily be removed and the instrument used as a simple, rather than an altazimuth, theodolite. Signed: '[star] ARyther ? fecit ? 1590 [star]'.

Jim Bennett

Istituto e Museo di Storia della Scienza, Firenze
Inventory no. 240

© Istituto e Museo di Storia della Scienza, Firenze. All rights reserved. Information and images provided here may not be reproduced in any form or by any means without the prior written permission of the museum.

Basic URL:

|| Introduction || Essay || Museums || Bibliography || Conventions || Credits || Privacy || Help ||
|Catalogue entries |Handlist || Makers || Places || Articles || Glossary || Search || Home ||