23:00, the office, one lamp
Nothing in it is random: two arms, two angles, two equations, and an energy that is conserved until the bearings spend it. For small swings it is tame: two modes, the arms together and the arms opposed, and every motion a sum of the two. Lifted high it is chaotic: the gap between two motions that begin a hair apart grows, on average, by the same factor in every equal time, so no hand lets go from the same place twice. Poincaré met this in the three-body problem in 1890; Lorenz found it in a model of the weather in 1963, and the Stadium Tray has it in its outline. Drawn here, for two equal bars: the path of the lamp, let go at rest with both arms 120° from the downward vertical, and again with the lower arm a hundredth of a radian further round, a little over a millimetre at the lamp. With arms of 125 mm that is one second: for the first half second the two lines are one, and by the end they are two arm’s lengths apart.
Objects · Desk instrument in brass and walnut
Double Pendulum
CHF 270 working price
For the last hour: let go twice from the same place, and watch it disagree with itself.
Two brass arms, one hung from the end of the other, on steel bearings over a walnut base, with a small lamp at the tip. Lift them and let go. Do it again from the same place, as nearly as a hand can: for half a second it repeats itself, then it does something else.
A study: nothing can be ordered yet. The photograph is a generated image, not a picture of a made piece or of a real person.
- Two arms of raw brass bar, 12 × 4 mm, 125 mm between centres, the second hung beside the first so that it can go right round; four shielded steel ball bearings, run dry
- A brass post on a turned walnut base 190 mm across, loaded with a steel plate, cork underneath: 320 mm tall, about 4 kg. It needs the weight: let go from high, the arms pull sideways about as hard as a kilogram pulls down, and a lighter stand would rock and walk. The arms clear the base at their lowest and reach 55 cm above the desk at their highest
- A small warm lamp at the tip of the lower arm, lit by one coin cell under a brass cap: turn the cap to light it. In a dark room, or in a long exposure, it draws the path. It is the only battery in the cabinet
- No catch and no stop: lift both arms and let go. The hand is part of the experiment; it is good to about a degree, and the pendulum notices far less
- Numbered under the base. Nothing on it is red
