1.1 Zucchi's attempt at a Herschel-type front-view reflecting telescope, 1616 2

1.2 Spherical aberration of a spherical concave telescope mirror. "Paraxial" rays are nominally at a negligible height from the axis 3

1.3 Two of Mersenne's designs for reflecting telescopes, adapted from "L'Harmonie Universelle", 1636, and King [1.1], compared with Galileo-type and Kepler-type refracting telescopes 4

1.4 (a) Facsimile of the Gregory telescope from "Optica Promota", 1663 (after Danjon and Couder [1.3]).

(b) Raypath of the Gregory form (after King [1.1]) 7

1.5 The Newton reflecting telescope, 1668 8

1.6 The Cassegrain reflecting telescope, 1672, (a) as drawn by de Berce.

(b) Raypath of the Cassegrain form (after King [1.1]) 10

1.7 John Hadley's 6-inch, f/10.3 Newton reflector, 1721

(courtesy Royal Astronomical Society, through Peter Hingley) . . . 12

1.8 The "Ramsden disk" (exit pupil) explained by Ramsden in 1775 (after King [1.1]) 15

1.9 Sir William Herschel (1738-1822) painted by L.T. Abbot in 1785 (courtesy Deutsches Museum, Munich) 16

1.10 William Herschel's "large" 20-foot focus telescope, aperture 18.8 inches (f/12.8), completed in 1784, (reproduced from an engraving of 1794, courtesy Science History Publications Ltd., Cambridge, England) 17

1.11 William Herschel's largest telescope: 4 feet in aperture, 40-foot focus (f/10), completed in 1789

(courtesy Deutsches Museum, Munich) 19

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