Accession No
6735
Brief Description
2 ¾ inch Gregorian reflecting telescope, by John Bird, English, mid-18th Century
Origin
England; London; the Strand; the Sea Quadrant
Maker
Bird, John
Class
astronomy; optical;
Earliest Date
1745
Latest Date
1776
Inscription Date
Material
metal (lacquered brass, steel); wood (mahogany); glass; ivory; enamel; paper (paper); cloth (velvet)
Dimensions
telescope (although adjustable): 515mm (width), 285mm (depth), 500mm (height); box (closed): 565mm (width), 223mm (depth), 145mm (height)
Special Collection
Provenance
Purchased in March 2021.
Inscription
J. Bird London.
[telescope]
John Bird
Mathematical
Instrument Maker,
at the Sea Quadrant, near the
new Exchange Buildings
in the Strand, London.
[trade label on the inside of the box lid]
NB. The Telescope with the
longest Eye-piece magnifies
54 times. The shortest 72
[hand written on trade label]
Description Notes
2 ¾ inch Gregorian reflecting telescope, by John Bird, English, mid-18th Century.
Lacquered brass Gregorian reflecting telescope, signed J. Bird, London. It has a 16 ½" (42cm) tube and single eyepiece, mounted on a folding tripod stand with an altitude adjustor and ivory turn-keys. It is stored in several pieces in a fitted mahogany box, the lid of which has a trade label for John Bird.
The 11 detachable pieces are -
.1 = body
.2 = cap
.3 = eyepiece
.4 = ivory turn-key
.5 = stand
.6 = knob from stand
.7 = box
.8 = fitted box piece
.9 = fitted box piece
.10 = box interior block
.11 = box interior block
Complete.
References
Events
Description
John Bird was one of the finest instrument-makers of his day. Although he is known to have produced a wide range of precision mathematical and optical instruments, very few telescopes signed by him survive. A hand-written note by Bird inside this instrument’s box reads “The Telescope with the longest Eye-piece magnifies 54 times. The shortest 72”.
19/11/2021
Created by: Morgan Bell on 19/11/2021
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 degraded quickly and were unable to transmit enough light. However, by the 18th 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.
This reflecting telescope was made by John Bird, a renowned London instrument maker. Before starting his own business, Bird worked for astronomical instrument maker Jonathan Sisson, the inventor of the modern theodolite, and clockmaker George Graham. Bird opened his own workshop in the Strand in 1745, making large instruments, such as an 8' transit instrument and mural quadrant for the Greenwich Royal Observatory, as well as smaller instruments. He also contributed to the first marine sextant. This telescope is signed J. Bird, which is rare.
15/04/2021
Created by: Morgan Bell on 15/04/2021
FM:47499
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