When London’s Millennium Bridge opened in 2000, it began to sway unexpectedly under the footsteps of the inaugural crowds. The danger of vibration in bridges was well known — the Albert Bridge (below) still bears a sign dating from 1873 that warns soldiers to break step while crossing. But the Millennium Bridge revealed a new phenomenon: As the pedestrians felt the bridge swing beneath them, they altered their movements to maintain their balance and began to sway together in step. This increased the amplitude of the bridge’s oscillations, a factor called synchronous lateral excitation.

The bridge was closed on opening day and underwent $9 million in repairs to increase its damping. It reopened in February 2002 and is now free of vibration, but it’s still known affectionately as the “wobbly bridge.”

Alexander Graham Bell believed that his greatest achievement was the photophone, a device that could transmit speech on a beam of light. The speaker’s voice would strike the back of a mirror, modulating a reflected ray. When the ray reached the receiver the process was reversed, producing sound waves.

“I have heard articulate speech by sunlight!” Bell wrote to his father in 1880. “I have heard a ray of the sun laugh and cough and sing! … I have been able to hear a shadow and I have even perceived by ear the passage of a cloud across the sun’s disk. You are the grandfather of the Photophone and I want to share my delight at my success.”

Bell hoped the invention might supplant expensive telephone lines, but it proved too vulnerable to weather conditions and fell by the wayside. That didn’t surprise the New York Times, which wrote in an editorial, “Until [the public] sees a man going through the streets with a coil of No. 12 sunbeams on his shoulder, and suspending them from pole to pole, there will be a general feeling that there is something about Professor Bell’s photophone which places a tremendous strain on human credulity.”

In 1947 two Harvard undergraduates, William Burkhart and Theodore Kalin, built a primitive machine for doing propositional logic. They had been taking a course in symbolic logic with Willard Van Orman Quine and were tired of solving problems with pencil and paper, so they set about making a machine that would do their homework automatically.

The result of their $150 investment was a small machine that could handle problems involving up to 12 terms in the propositional calculus. The “Kalin-Burkhart machine” marks a milestone in the development of logic machines, but working in the machine’s language is so laborious that using a pencil is faster.

“It is interesting to note that when certain types of paradoxes are fed to the Kalin-Burkhart machine it goes into an oscillating phase, switching rapidly back and forth from true to false,” noted Martin Gardner in Logic Machines and Diagrams (1958). “In a letter to Burkhart in 1947 Kalin described one such example and concluded, ‘This may be a version of Russell’s paradox. Anyway, it makes a hell of a racket.'”

An epic contest from the Annual Green Fair and South West Scythe Festival in Somerset, U.K., June 2010.

One commenter wrote, “Now we know why Death carries a Scythe, not a brushcutter.”

This Victorian artificial arm and hand is in the collection of the London Science Museum. “The arm is amazingly versatile,” writes Ben Russell in Robots (2017). “The elbow can be locked in several positions, and the fingers articulated using a brass button in the wrist. It is also heavily decorated in the neo-Gothic style. Rather than being covered up, this arm would be out on view, making its wearer a true man-machine.”