Compare ... the various quantities of the same element contained in the molecule of the free substance and in those of all its different compounds and you will not be able to escape the following law: The different quantities of the same element contained in different molecules are all whole multiples of one and the same quantity, which always being entire, has the right to be called an atom.

To Avogadro and Cannizzaro, as to Couper and Kekulé, the molecules and atoms considered in this great theory were real objects: they were thought of the same way as one thinks of tables and chairs.