Rough sketch of James Nasmyths' apparatus by which most perfect sound speculae may be cast with absolute certainty 1879
The first 48-inch speculum mirror cast with metal cover by Sir William Herschel in 1785 for his 'Forty Foot' telescope at Slough, England. Original mirror for William Herschel's forty-foot telescope, 1785. 1785
Experimental speculum of 6 inches aperture and 24 inches focal distance, cracked across and bound together with string Experimental speculum of 6 inches aperture and 24 inches focal distance 1840-1870
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
Elliptical plane mirror (diagonal flat for Newtonian telescope) minor axis 1 1/2", major axis 2" in (full) soldered in usual way to circular brass disc, cylindrical cover of brass 1 3/4" deep, cover of brass 1 3/4" deep, cover and brass disc inscribed 1 "A4" Elliptical plane mirror (diagonal flat for Newtonian telescope) minor axis 1 1/2" 1780-1820
Oval shaped secondary speculum mirror with cover, from the 6-foot Rosse telescope Oval shaped secondary speculum mirror with cover 1845-1850
Experimental compound speculum mirror of 2 feet diameter, made by the 3rd Earl of Rosse. The 9 segments of speculum metal, are held in an alloy of copper and zinc. Experimental compound speculum mirror of 2 feet diameter 1840-1845
Two plane speculums by Lassell, with Lassell's M.S. directions Two plane speculums by Lassell 1840-1850
Optical parts of Lassell's telescope:- prism for 9-in reflector in green cardboard box; 3 multiple eyepieces; 5 small eyepieces; speculum for Newtonian finder in tin case 4 eyepices; 4 diaphragms (3 in two tin cases and one in wood case with metal lid) Optical parts of Lassell's telescope 1840-1850