716 SPHERES: INSULATED (478) 2/4 19th C.
Base diameters 122, 124; sphere diameters 79, 91; heights
330, 342
Turned walnut bases with solid glass pillars and brass spheres at the top.
Both bases have one side cut square so that the spheres can be brought
to touching point.
717 LICHTENBERG FIGURES (479) before 1862
Base of tower 225 x 178; height 370; plates 152 x 152
716
Twelve copper plates, coated with pitch, are contained in a rough, pine-
wood tower. A round pine box contains six wrapping cloths, tied with
string, and holding powder. Some are stained pink; the powder is a mixture
of red lead and sulphur. The use of this apparatus is discussed in
Van der Willigen (1862); “De Lichtenbergsche figuren”.
Georg Christoph Lichtenberg (1742-1799), a professor of
physics at Gottingen University, discovered by 1777 that an insulating
surface, such as pitch, when coated with a fine powder and placed
between electrodes and a high voltage passed, will exhibit characteristic
patterns in the dust, which differ for positive or negative electricity;
Lichtenberg (1777). The patterns are known as ‘Lichtenberg figures’. In
truth, he had found the basics of xerographic copying. Deschanel
(1877), 582, fig. 393; Guillemin (1891), 194-198; Magnusson (1928);
Mautner & Miller (1952).
9
9
n1
* A 718
718 NON-CONDUCTIVITY IN VACUUM
(1012)
3/4 19th C.
Unsigned; probably French
Base diameter 122; board 127 x 142; height to board 226
A circular brass base and pillar support an ebonite rectangular board
with copper strips on two sides, each holding two wire terminals, a brass
post for a rod, and a holder with a copper spike (length® 6) attached.
The apparatus is said by Deschanel to have been constructed by
Alvergniat; it demonstrates the non-conductivity of a perfect vacuum.
The two high terminals are used to support a glass Geissler tube with
two platinum wires sealed in the ends and set to within 0.1 mm of each
other. The glass tube is evacuated to a very high degree by a Geissler
pump, and it is heated to near the fusion point of glass to absorb any
remaining air. When connected to an electrostatic generator, the arc is
not formed between the electrodes in the tube, even though the gap is
very small, but the spark occurs in air between the copper spikes set at
a much greater distance apart. Described in Deschanel (1877), 551-
552, f i g . 368.
719 ELECTROPHORUS PLATES (483) 3/4 19th C.
1. Glass, ground both sides; diameter 430; thickness 9.
2. Tinplate sheet; diameter 500.
3. Black ebonite sheet (from a Wimshurst machine);
diameter 410.
4. Wood plate, covered in tinfoil, with three holes through which
passes string to an ebonite knob; diameter 350. Deschanel
(1877), 543-544, fig. 358; Guillemin (1891), 187-191.