Redefining Reality - The Intellectual Implications of Modern Science

The big breakthrough came with the work of the British chemist
John Dalton and the French researcher Joseph-Louis Proust, who
independently discovered that whenever elemental substances are
to get out a given amount.
The ratio of the amounts of stuff in to get one unit of stuff out
is always a ratio of counting numbers: 2 to 1, 3 to 1, 4 to 1
to 3, and so on.
If nature is using counting numbers, it is probably counting
something, which means that there must be something to
be counted. Perhaps elemental substances are made up of
countable bits. Chemists grew nervous that atoms were making
their way back.
The Italian chemist and atomist Amedeo Avogadro believed that
the work of Dalton and Proust showed something important:
an integer’s weight of a new substance was that there were basic
building-block things joining with other basic building-block things
to create hybrid things. He called the bits of elements atoms and
labeled the combinations molecules.
Avogadro proposed that “equal volumes of all gases, at the same
temperature and pressure, have the same number of molecules.”
Before Avogadro, we could use the idea of atoms as a heuristic, a
way of thinking that gives us an easy image to hold in our minds.
But chemists were careful not to mistake this mental picture for
reality. It was Avogadro who took the next step and introduced
the number of molecules, and you cannot have a number of things
without having those things.
When Avogadro’s law was added to the other gas laws, it became
possible to formulate a new combined law known as the ideal gas law:
For any gas, the pressure multiplied by the volume is proportional to
the number of molecules multiplied by the temperature.
50