Graham's law has come to denote an important class of finely divided materials. Around the time Graham did his work, the concept of molecular weight was being established largely through the measurements of gases. Daniel Bernoulli suggested in 1738 in his book Hydrodynamica that heat increases in proportion to the velocity, and thus kinetic energy, of gas particles. Italian physicist Amedeo Avogadro also suggested in 1811 that equal volumes of different gases contain equal numbers of molecules. Thus, the relative molecular weights of two gases are equal to the ratio of weights of equal volumes of the gases. Avogadro's insight together with
History of molecular theory Determining the Relative Masses of the Elementary Molecules of Bodies", he essentially states, i.e. according to Partington's "A Short History of Chemistry", that: Note that this quote is not a literal translation. Avogadro uses the name "molecule" for both atoms and molecules. Specifically, he uses the name "elementary molecule" when referring to atoms and to complicate the matter also speaks of "compound molecules" and "composite molecules". During his stay in Vercelli, Avogadro wrote a concise note ("memoria") in which he declared the hypothesis of what we now call Avogadro's law: "equal volumes of gases, at the same temperature and pressure,