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Concave Rowland diffraction grating on speculum metal

1894

Plane Rowland diffraction grating on speculum metal

1895-1909 (estimated)

Concave Rowland diffraction grating on speculum metal

1898

Diffraction grating area 5 cm by 4.5 cm on 8 cm by 7.5 cm (approx) block of speculum metal

1905-05-26

Concave diffraction grating on speculum metal

1910-1948 (estimated)

Concave diffraction grating on speculum metal

1926, May

diffraction grating on speculum metal, gra

1881

Anamorphic picture, early 18th century, with cone mirror, wooden cover and two anamorphic pictures

1745-1753

Heliostatic mounting

1795-1805

Heliostat, c. 1752.

1747-1757

Reflecting telescope by William Herschel, 1783-1785

1783-1785

Primary metal speculum mirror with central hole

1840-1850

Concave Rowland-type diffraction grating on speculum metal

1882-1909 (estimated)

Concave Rowland diffraction grating on speculum metal

1894

Concave Rowland diffraction grating on speculum metal

1899

Concave Rowland-type diffraction grating on speculum metal

1882-1899

Concave Rowland-type diffraction grating on speculum metal

1926, April

Concave Rowland diffraction grating on speculum metal

1882, Nov 6

Anamorphic picture

1745-1752

Cassegrain reflecting Telescope of 2 1/2-inch aperture

1756-1758
Gregorian reflecting telescope of 2 1/2 inch aperture and 18 inch focal length by Benjamin Martin, London, on an altazimuth stand with a folding claw foot tripod and oak case.

Gregorian reflecting telescope of 2 1/2 inch aperture and 18 inch focal length by Benjamin Martin

1738-1777
Gregorian reflecting telescope of 3-inch aperture by James Short, London [138/878 = 12] (138th of 12 inch type out of 878 made) plus 1 spare eyepiece, no stand. [replica mahogany (wood) stand was made in workshops]

Gregorian reflecting telescope of 3-inch aperture by James Short

1753-1755
Objective mirror assembly for a reflecting microscope comprising large aspheric aluminised speculum metal primary mirror made by I. H. Ford on C. R. Burch's mirror figuring machine at Bristol (Inv. No. 1986-113), plus a small aluminised spherical mirror, made from part of a ball bearing, in a kinematically designed mount allowing backlash-free adjustment of the primary mirror in the x and y directions and the secondary mirror in the z direction, made between about 1954 and 1964. Also an engineering drawing of the assembly.

Objective mirror assembly for a reflecting microscope

1954-1964
Concave Rowland-type diffraction grating on speculum metal, grating area 139 x 57 mm, with scratched markings reading 'Ruled at J. H. U. 1934 / R. W. Wood & W. H. Perry / 30,000 lines per inch / 21' radius of curvature'. (J. H. U. = Johns Hopkins University.)

Concave Rowland-type diffraction grating on speculum metal

1934
Two plane speculums by Lassell, with Lassell's M.S. directions

Two plane speculums by Lassell

1840-1850
Brass Gregorian telescope of 3 1/2 inch aperture by B. Martin, London on altazimuth stand with claw foot stand, 2 eyepieces and a wooden case. The instrument was used by John Winthrop to observe the 1761 transit of Venus. Given to Harvard College by Thomas Hancock of Boston Mass., it is thought to be the only instrument to survive the fire of 1764.

Brass Gregorian telescope of 3 1/2 inch aperture by B. Martin

1757-1761
Oval shaped secondary speculum mirror with cover, from the 6-foot Rosse telescope

Oval shaped secondary speculum mirror with cover

1845-1850
Nine inch mirror of speculum metal (exact diam" 8 15/16 in) in tin cell with close fitting cover 9 1/2" diam, 1 1/2" deep, focal length 10' 1", cell and cover each painted " J"

Nine inch mirror of speculum metal (exact diam" 8 15/16 in) in tin cell with close fitting cover 9 1/2" diam

1780-1820
Gregorian reflecting telescope of 2 1/8 inch aperture with shagreen covered tube and wooden case. The telescope has a ball and socket stand with a claw foot tripod and a mahogany stand made by the Science Museum workshops. Attached to the wooden stand is another ball and socket mounting with screw stand added by Mr T H Court, the donor.

Gregorian reflecting telescope of 2 1/8 inch aperture with shagreen covered tube and wooden case

1724-1731