Accession No

0833


Brief Description

circular logarithmic scale “circles of proportion”, and horizontal instrument, by Elias Allen, designed by William Oughtred, English, c. 1635


Origin

England; London; The Strand


Maker

Allen, Elias [maker] Oughtred, William [designer]


Class

mathematics; calculating


Earliest Date

Jan. 1, 1635


Latest Date

Dec. 31, 1635


Inscription Date


Material

metal (brass)


Dimensions

diameter 314mm


Special Collection

Cavendish Collection?


Provenance

probably part of the W.H. Wollaston collection although the information in the history file is confused between this collection and the Hutchinson collection. Cambridge University Reporter, 20 May 1876, p.498, suggests that it is from the Wollaston collection, transferred to the Cavendish in that year.


Inscription

‘Elias Allen fecit’ (reverse)


Description Notes

Circular logarithmic scale “circles of proportion”, and horizontal instrument, made by Elias Allen, designed by William Oughtred, c. 1635.

Circular brass disc with suspension ring and shackle. Circles of proportion has double index arm, other side has single index arm.
Obverse: concentric scales reading from the rim inwards.
1. log scale of sines, divided anticlockwise [6˚] - 90˚, numbered by 10˚; 6 - 60˚ subdivided to 5´, 60˚ - 70˚ subdivided to 10´, 70˚ - 80˚ subdivided to 30´, 80˚ - 85˚ subdivided to 1˚.
2. log scale of tangents split over two circles, divided anticlockwise[6˚] - 45˚ and 45˚ - 84˚, numbered by 10˚ and at 45 and 84; subdivided to 5´.
3. log scale of numbers, divided anticlockwise 1 10,numbered by 1; 1 - 7 subdivided to 0.01, 7 - 10 subdivided to 0.02.
4. scale of equal numbers, divided anticlockwise 1 - 10, numbered by 1, subdivided to 0.01.
5. log scale of tangents, divided anticlockwise 84˚ - [89˚ 20´], numbered by 1˚, subdivided to 5´.
6. log scale of tangents, divided anticlockwise [40´] - 6˚, numbered by 1˚, subdivided to 5´.
7. log scale of sines, divided anticlockwise [40´] - 6˚, numbered by 1˚, subdivided to 5´.
Central three circles form a nocturnal:
circle of hours, divided anticlockwise 1 - 12, 1 - 12, numbered by 1, subdivided to 15 minutes.
circle of months with named months, numbered clockwise 10-20-28, 30 or 31 as appropriate, subdivided to 1 day.
Circle of important stars.
Two index arms with bevelled edges, moving together with friction-tight adjustment in a flat hinge; marked ‘S, T, T, N, E, T, T, S’ to correspond to the log scales.
Reverse: Oughtred’s horizontal instrument for 52˚ N.
Degree circle divided 90˚ - [0] - 90˚ [ 0] - 90˚, numbered by 10˚, subdivided to 15´.
Lines of declination, uncalibrated, tropic to tropic across the equator, divided to 1˚ with 30´ subdivisions marked on crossing lines.
Circle of ecliptic with named months, numbered 10-20-28, 30 or 31 as appropriate, subdivided to 1 day. Equinoxes at 10 March and 12 September.
Hour lines perpendicular to lines of declination and only drawn between the Tropics; numbered by hour, subdivided to 4 minutes.
Construction line down centre of instrument with centres from which circles of declination have been drawn. Three named points: ‘PII’, ‘PW’, ‘PI’.
Single index arm with bevelled edge, marked for solar altitude towards centre, divided [0] - [62˚], numbered by 10˚, subdivided to 30´.

Condition good; complete.

[NOTE: On 15/04/2015 XRF analysis was conducted on this instrument. Results and analysis are given in the ‘Notes’ field.]


References


Events

Description
John Napier’s invention of logarithms, published in 1614, was acclaimed throughout Europe. It provided a new and immensely powerful computational tool. In 1623 Gunter suggested that Napier’s “artificial numbers” could be usd by sailors in an instrumental form. He set out logarithmically divided lines of certain trigonometrical functions on the limb of a cross-staff. William Oughtred improved Gunter’s idea and invented the first circular and linear logarithmic slide rules. The detailed design of Oughtred’s “circles of proportion”, published in 1632, was influenced by the London instrument-maker Elias Allen. At Allen’s request, Oughtred re-designed the circular slide rule so that the pairs of concentric sliding scales, which were demanding to construct, were replaced by a single set of scales and a pair of radial arms.


FM:39866

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