The meicr rule ai upper left is jointed in the middle.
335 MISCELLANEOUS ACCESSORIES 1790-1795 (508/e) Fig. 295
A collection of discharging points, ball and pear-shaped conductors of various
materials, conductors, rubbing pads, etc. Some of the items resemble the accessories
associated with a Nairne Patent Electrical Machine (Cat. 282), and a full set is
illustrated in the catalogue of the Görlitz museum. Other pieces resemble items
illustrated in volume ix of the Verhandelingen.
Van Marum (1795) III, fig. 11, 14; Görlitz (1953) 15, 34.
336 SPARK CHAMBER 4/4 18th C. (533) Fig. 297
Overall height 420, diameter of sphere 85.
A copper sphere is held by a collar in a stand made of copper; from the top rises a
turn-cock and a long glas§ tube, with two wires inside that nearly meet at the midpoint.
At the side of the sphere there are two short copper tubes, one of which has
a glass tube running through it with a thin brass rod at its centre.
Neither the purpose nor the period of this piece of apparatus can be identified. It
may have been used for an electric discharge in a vacuum.
337 DISCHARGER 4/4 18th C. (907) Fig. 298
Possibly by John Cuthbertson
Baseboard 200 x 9j| overall height 140, diameter of spheres 75.
Two copper spheres are each mounted on turned brass supports, with a terminal in
each stem. They are fixed to a baseboard, and so can constitute a spark gap of fixed
length. The diameter of the spheres is three inches in English measure, and together
with their character, the work of John Cuthbertson is suggested.
G A L V A N I C E L E C T R I C I T Y
Van Marum had an interest in current electricity, but no extant instruments can be identified as
purchased by him. There follow four entries to represent this topic that could have been obtained
during the first quarter of the nineteenth century.
33« VOLTAIC PILE >/4 19th C. (575) Fig. 299
Baseboard 220 x 220, overall height 250; plates 60 x 60, height of pile 165.
This is a small, simple voltaic pile, composed of a total of 4g pairs of plates. It
cannot be exactly dated. In his Inventory, 61/1, 2, Van Marum records two massive
piles, one of 200 pairs of plates 25 inches square. Fredrick Accum advertised, in
1805, Galvanic batteries from one to ten guineas.
In 179°) Luigi Galvani ||j 737—1798) observed that newly dissected frogs’ legs
twitched when an electrostatic machine was working. The phenomenon was investigated
by Alessandro Volta (1745-1827), whose letter to Sir Joseph Banks, of
20 March, 1800, was published later the same year by the Royal Society. Volta
used copper and zinc plates, with cloth moistened by salt water between them. Van
Marum entered into correspondence with Volta, and the twenty-three letters have
been published by J. Bosscha.
Volta (1800;; Accum (1805); Bosscha (1905).