Sprinkle sand on a vibrating plate and it forms patterns that reveal where the plate is still

science & techThe Public Domain Review1787 · Germany

Sprinkle sand on a vibrating plate and it forms patterns that reveal where the plate is still

the gist

When a plate is bowed at its edge or made to vibrate, it does not move evenly across its whole surface. Some areas move up and down strongly, while lines between them stay still; these are called nodal lines. Loose sand or powder on the plate gets thrown off the moving areas and collects along the still lines, forming a shape. Robert Hooke noticed the effect in the 1600s with a flour-covered glass plate and a violin bow. In 1787 the German physicist Ernst Chladni systematically recorded these patterns in his book Entdeckungen über die Theorie des Klanges. The shapes now bear his name as Chladni figures.

how it works

When a plate vibrates at a particular frequency, parts of it move in opposite directions while other parts stay still. Sand is pushed away from the moving regions and settles along the still lines, so the pattern marks the places where the plate barely moves.

so what

Chladni figures showed that sound and vibration produce visible geometry, a key idea behind acoustics and the design of musical instruments. The method is still used to study how plates and membranes vibrate.

fun fact

Chladni originally trained in law before turning to physics and music.

D. W. Griffith’s A Corner in Wheat (1909)

the gist

In 1909 D. W. Griffith made a 14-minute film about a speculator who corners the wheat market and doubles the price of bread. A farmer sows his field while a 'Wheat King' gambles in the Chicago wheat pit; bakers raise the loaf from five cents to ten and the poor line up for bread. Griffith cut back and forth between the farm, the feast and the breadline, a technique called parallel editing, so audiences saw both ends of the economy at once. The film drew on Frank Norris's stories and on a real scheme: months earlier Chicago financier James Patten had cornered wheat, sent bread prices up and made about $5 million, roughly $185 million today.

how it works

To corner a market, a trader buys up most of the available supply and the futures contracts that promise more. Anyone who has to deliver the commodity must then buy from the cornerer at whatever price is demanded. The trader profits until the stock is released or the scheme collapses.

so what

A century on, it still shows how markets can be rigged by someone who controls supply, and how the people at either end, farmers and eaters, pay for it. It also helped establish editing as a way to argue a point, not just tell a story.

the bigger pattern

Corners have recurred whenever supply could be locked up, from the Hunt brothers' attempt on silver in 1979 to 1980 to the 'Black Friday' gold panic of 1869. Many such schemes end by collapsing, and the response is often new rules on speculation.

fun fact

In the film the Wheat King dies by falling into a grain elevator and being buried in the wheat he hoarded, an ending borrowed from Norris's novel The Octopus.

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