294 AURORA JAR % 18th C. ( 5 3 g § Fig. 261
The glass jar (height 310, diameter 2(56), has a narrow neck on which rests a brass
disk. Through this passes, via an air-tight gland, a brass rod carrying a brass sphere
(diameter 85). On top of the rod is a handle for positioning the sphere above a base
plate.
Inv. 56/12
295 AURORA JAR */4 18th C. (536) Fig. 262
Mounted on a mahogany tripod stand, the glass jar (overall height 440, diameter
160) is sealed with a brass disk, from which is suspended a copper ring. Above the
disk is a screw terminal. In the base are a copper annulus and a short glass tube bearing
a conical copper cap.
Inv. 56/7
296 AURORA JAR % 18th C. (539) Fig. 262
Mounted on a mahogany tripod stand, the bulbous glass jar (overall height 350,
maximum diameter 230) is sealed with a brass disk, from which hangs a vertically-
mounted copper ring with a cusped interior. Above the disk is a screw terminal. On
the base is a tripod-mounted horizontal ring with a cusped edge. From one side of
the base rises an insulated brass rod, terminating in a ball with a wire extending
towards the centres of the two rings.
Im. 56/8
297 AURORA JAR % 18th C. (534) Fig- 262
Mounted on a mahogany tripod stand, the glass jar (overall height 400, diameter
at base 140), is sealed by a brass disk with a small brass sphere mounted above it.
In the base is a copper hemisphere.
Inv, 56/g
298 BASE PLATE % 18th C. (535)
A circular brass disk with a lip (diameter 18® on a brass pillar with stop-cock, is
supported by a turned mahogany base (overall height 230). This serves as a base-plate
for aurora jars undergoing evacuation.
299 ELECTRIC BAROMETER pre 1790 ;|i 159) Fig. 263
A mahogany b3fterdj|k;j5 x 150) holds at either end an insulating pillar topped by
a brass ball with a small hole. Between the pillars, two pitch disks are set into the
wood that support glass beakers. The ends of a long U-shaped glass tube dip into
theses ^overall lieight of the apparatus 895), the tube being held by a mahogany
framework (height 4.80). According to the Inventory, the apparatus is after Wilson,
and demonstrates the difference between the glow discharge at the positive and
negative terminals,
Van Marum js>ld to Teyler’s on 19 November, 1790 for ƒ 14, “ De Dubbelde
Quikbuis van Wilson op een voef ’ (MV), _
Inv. 56/15
300 ELECTRIC BAROMETER c. 1790 (1160)
Similar to the above, Cat. 299 (baseboard 355 x 95, height of frame 390, overall
height 835^H
Inv. 56/15
301 FLICKER JAR % 18th C. (487) Fig. 264
The glasBar (height 490, diameter 185).; is helically banded inside and out with
foil. A brass ball at the top is connected by a strip to the upper terminal on the
banding. At the bottom of the banding is a second terminal. The jar rests on a round
wooden platform.
302 FLICKER JAR % 18th C. (488) Fig. 264
The glass jar 'height 225, diameter i6o®is foiled on the inside, and on the outside
where the foiling is arranged in a brick-work pattern. The neck of the jar is sealed
with a wooden disk, through the centre of which runs a brass rod. Above the disk is a
small inverted glass, flask.