In the spring of 1654, German scientist Otto von Guericke staged
a dramatic demonstration of his new invention, the vacuum pump.
Guericke was the mayor (Bürgermeister) of Magdeburg, and he
arranged for a public demonstration in the town square. Two
teams of 15 horses would try to pull apart two 20"-diameter
metal hemispheres. The hemispheres were not bolted, welded,
glued, or otherwise mechanically connected to one another.
Instead, the air inside the sphere had been evacuated by means
of von Guericke’s new vacuum pump. Strain and pull as they
might, the force of the vacuum was stronger than the 30 horses —
the teams could not part the sphere. The Magdeburg Hemispheres,
as they came to be known, were a pair of large copper
hemispheres with mating rims. Von Guericke applied a thick
coating of grease to the rims, attached his new vacuum pump
apparatus, and pumped out a good bit of the air, producing a
strong vacuum inside. How hard would those horses have to pull
in order to separate the hemispheres? To figure