Accession No
0741
Brief Description
reflecting telescope, Newtonian 5-foot, that belonged to English mathematician Robert Smith, by George Hearne, English, 1730 (c)
Origin
England; London
Maker
Hearne, George
Class
astronomy; optical
Earliest Date
1730
Latest Date
1730
Inscription Date
Material
wood (oak); metal (brass); string
Dimensions
l (tube) 1840 mm; h (stand) 980 mm primary mirror diameter 151mm; thickness 25mm; handle length 93mm
Special Collection
Provenance
Simpson (2009, p.438) states that this instrument was formerly the property of the English mathematician Robert Smith (1689-1768), who presented it to Trinity College, Cambridge.
Inscription
G: Hearne
London
Fecit
Description Notes
Reflecting telescope, Newtonian, 5-foot focus, by George Hearne, English, c. 1730.
Newtonian reflecting telescope. Octagonal wooden tube. Hinged opening for access to objective. Brass plate (with 2 screws) for eye piece (missing) slides in brass mount with wooden knob for focussing. Wooden tube for finder mounted on top with brass objective end and cover. No optics. 2 brass rods for mounting on stand. Brass plate with 2 screws (function unclear). Brass makers plate. Paper label stuck on. Wooden stand with brass fittings. Reinforced tripod base carries telescope platform which pivots (restricted travel) about vertical axis at one end. Wooden knob controls vertical motion via string. Brass knob for pivoting motion (incomplete). Drawer (with key) contains miscellaneous wooden and brass pieces. Primary mirror (tarnished) with turned wooden handle.
good/fair condition
1 metal sheet and 1 wooden box containing ?lead balls are in the wooden tube for ballast - MUST be removed before dismantling and moving the telescope.
References
Events
Description
Isaac Newton built the first reflecting telescope in 1669. Unlike a refracting telescope a reflecting telescope uses concave mirrors to focus light. The great advantage of using mirrors is that all colours of light are reflected equally. This was an improvement on the refracting telescope which used lenses to focus light. Here the light refracted at different angles to create a distorting fringe of colour around the image being observed.
At first high quality reflecting telescopes were difficult to make as the mirrors available to use degraded quickly and were unable to transmit enough light. But by the eighteenth century methods of making mirrors had improved and instrument makers such as James Short had created hundreds of reflecting telescopes for sale.
There are three types of reflecting telescope: the Gregorian, the Cassegrain and the Newtonian. Both the Gregorian and Cassegrain telescopes are pointed directly at the object being viewed. But the Newtonian has a secondary mirror set at 45° to the objective so the observer stands at right angles to the telescope. Today modern telescopes (with apertures greater than one metre) are reflecting telescopes. Various innovations make them more powerful and accurate. Computer controlled deformable mirrors can correct against changes due to atmospheric conditions or faults in the material.
Created by: Jenny Downes
FM:39917
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