Michael FaradayAll Quiet In Here.

The sticker says All Quiet In Here. Michael Faraday went and checked.

In the lecture room of the Royal Institution he set up an insulated cube twelve feet on a side: a light wooden frame strung with copper wire and covered in paper and bands of tin foil. He charged the outside until sparks and brushes darted off every part of its surface. Then he wrote: “I went into the cube and lived in it.” With lighted candles, electrometers and every other test he had, he “could not find the least influence upon them.”

The reason is that charge on a conductor moves until the whole conductor sits at one potential, and it ends up on the outer surface. In electrostatic equilibrium the field inside an empty cavity in a closed conductor is exactly zero, whatever is happening outside. Gauss's law, above, is the modern way to say it. Faraday showed it with instruments, and with himself as the test subject.

A mesh works nearly as well as solid metal, as long as the holes are small compared with the waves being blocked. That's why a microwave oven door is a mesh you can see through. It's also why a hard-topped car is a decent place to sit out a thunderstorm: the US National Weather Service notes that the outer metal shell protects the people inside with the windows closed. The rubber tyres have nothing to do with it.

The cube is usually dated to 1836, and he published it in 1838 in the eleventh series of his Experimental Researches in Electricity. Our cube is drawn smaller to fit the sticker.

The tea is our addition. The calm is his.