Purchased from Funckler, Haarlem, invoiced January 1886, prism Dfl.
25; lens Dfl. 30. Ducretet founded his firm in 1864; see Brenni (VIII).
549 LENSES (342, 343, 347, 348, n.n.) c. 1869
549
342 Bi-convex lens (diameter 290) in brass frame swung on brass
semi-circle, and mounted on a turned mahogany stand with
turn-nut to hold brass spike. Focal length 870 (1.15 diopters).
Base diameter 180, height 240.
343 Plano-convex lens (diameter 230) in brass frame on a mahogany
stand. Focal length 1.78 m (0.56 diopters). Base diameter
176, height 250.
347 Plano-convex achromatic doublet (diameter 54, thickness 8).
Museum records describe it as by J.G. Hofmann, Paris.
Written in pencil round rim of lens: J.G. Hofmann Paris 1869.
Focal length 350. Brass stand, height to knurl 165. Air space
between lenses is deliquescent.
348 Plano-convex achromatic doublet (diameter 80). Mounted on
stand with iron foot (diameter 100, height 220), painted
bronze. Focal length 360.
n.n. Plano-convex achromatic doublet (diameter 75). Mounted on
stand (overall height 310) with circular iron base (diameter
100), bronze-lacquered. Focal length c. 350.
550 LENSES (770, f? 3 , 774, 775, 839, 840), ' 1885
550 (774), (839) 551 (771) (773)
770 Biconvex lens (diameter 125) in square blackened deal mount
(192 x 190). Stand with three levelling screws, and ivory turn-
button on brass band to grip. Focal length 270. Records give a
date of 1885.
773 Two lenses (aperture 38, focal length 280; aperture 40, focal
®?4" length 130) set in discs (diameter 132) finished in black
cracknel. Short brass stands (base diameter 172) accept the
pins attached to the discs. Records give a date of 1885.
775 Biconvex lens (diameter 72, focal length 170). Records give a
date of 1885.
839 Biconvex lens (diameter 68, focal length 240) in a black wooden
frame on cast brass stand (base diameter 72). Frame held by
long brass rod (length 250). ;
840 Plano-convex lens (diameter 155; focal length 170) in wooden
frame (diameter 205), with brass fitting on one side for
mounting on a stand.
551 CYLINDRICAL LENSES (771,772, 4/4 19th C.
551
K . Cylindrical lens (37 x S a fin a rotating frame set in a disc of
black brass. Supported on a pillar via a ball and socket joint
(height 250) over a leaded brass base (diameter 90). Scratched
on the frame (not by manufacturer) is: Bi-convex cilinder ± 23
C” Focus. Purchased 1885.
I l l Two cylindrical lenses.
1. Mounted in black wooden frame; lens aperture 45 x 35;
frame 127 x 85. FocaSingth 230.
2. Mounted in blackened metal frame with brass screw attachment
at bottom; lens 48 x 45; frame 130 x 135. Focal length
280 (3.57 diopters). Purchased 1885-
888 Cylindrical lens mounted in brass plate with one end bent over
and shaped as if to fit some other apparatus. Raised circular
mount for lens (recessed other side). Plate 152 x 102; mount
diameter 42; lens 23 x 23. Focal length 40.
552 MIRRORS (317, 887) 3/4 19th C.
317k > Two silvered glass convex mirrors mounted in wood, painted
black, and fixed back to back on a thin rod with brass fitting
and wooden base. Frame diameter 102, mirror diameter 72,
height 220, base diameter 45.