The first step on the
road to a thermometer was taken by one Philo of Byzantium , an engineer, in the second century BC. He took
a hollow lead sphere connected with a tight seal to one end of a pipe, the
other end of the pipe being under water in another vessel.
To quote Philo: “…if
you expose the sphere to the sun, part of the air enclosed in the tube will
pass out when the sphere becomes hot. This will be evident because the air
will descend from the tube into the water, agitating it and producing a
succession of bubbles.
Now if the sphere is
put back in the shade, that is, where the sun’s rays do not reach it, the water
will rise and pass through the tube
“No matter how many
times you repeat the operation, the same thing will happen.
In fact, if you heat
the sphere with fire, or even if you pour hot water over it, the result will be