720 SPARK MEASURER (521) 3/4 19th C.
Base diameter 116; overall height 230
Circular base of African mahogany and glass tube with brass fitting support
a rectangular brass plate over which moves a dovetailed platform
operated by rackwork. This platform carries a dovetailed support for
two glass and brass conductors, whose positions can be adjusted by
screws, pressure being sustained by a flat, brass spring. The glass conductors
end in terminals, and from each of these, bent brass conductors
covered in red wax arch upwards, with small polished discs at the ends,
between which the spark jumps.
720
721 SPARK DURATION DEMONSTRATOR
(522)
before 1859
Base 120 x 70; diameter of disk 180
Apparatus consists of a mahogany base, bearing two glass and brass pillars,
a mirror on a stand, a brass wheel and a paper-covered disc, with
blue/white segments on one side, and black/white on the other. The
disc rotates to show the duration of an electric spark, which is produced
between the two rods that are held on the glass pillars. When rotated,
the impression of the disk is grey; a spark makes the sectors stand
out sharply. As a discharge occupies about 1 millionth of a second, this
disc cannot possibly give a measure of the effect, merely an illustration.
722 SPARK MICROMETERS (551,552) 3/4 19th C.
551 Rectangular base (160 x 93) of African mahogany, supporting
a brass bar on which are two glass pillars, one fixed, one movable,
- in brass fittings. Both pillars end in terminals for clamping
rods that adjust the two spheres facing each other. Ivory scale
on base, 0 to 105 mm by halves. Scale same as on 724; probably
same maker. Overall height 1 8 7 ^ |
552- Round mahogany base (diameter 118) supports a glass pillar
with rectangular brass platform, above which are mounted one
fixed and one movable glass rods, tipped with double wire terminals,
and topped with push-on brass spheres. On the platform
is a silvered, millimetre scale, 0 to 70 mm, and a vernier,
measuring tenths. A long screw for adjustment. Overall height
202. P.J. Kipp sold “1 vonken-micrometer” in May 1869 for
Dfl. 32.
722 >T': 722
723 SPARK MICROMETER (1006) 1/4 20th C.
Unsigned; by J. van Waveren
Base diameter 138; overall height 234
Round mahogany base, brass mounts, and ebonite pillar to a platform
over which moves ijp^a dovetail a brass bar, supporting a glass pillar.
Movement controlled by rackwork, cut diagonally, and a knurled knob.
The movable and the fixed pillars have knobs with wire terminals.
There is a millimetre scale, 0 to 5 by ones. Museum records give the
maker as J. van Waveren, who was the amanuensis in the Teyler’s laboratory
from 1900 until 1936.