Henry Cavendish hung a rod carrying two small lead balls near two large lead spheres. Their tiny gravitational pull made the rod twist slightly. To avoid disturbing it, he watched from outside the room through a telescope. He concluded that the Earth is about 5.5 times denser than water, within roughly 1% of today's value.
Cooled below −183 °C, oxygen turns into a pale blue liquid. Pour it between the poles of a strong magnet and, instead of flowing away, it hangs suspended between them. The reason lies in its unpaired electrons, which respond to the magnetic field. Liquid nitrogen, by contrast, is colourless and pours straight through.
In 2012, Felix Baumgartner jumped from a capsule hanging beneath a balloon, about 39 kilometres up. In that extremely thin air almost nothing slowed him down, and he reached around 1,358 km/h in free fall, or Mach 1.25. He became the first person to exceed the speed of sound with nothing but his own body.