There was a fundamental difference between the atomic theory of Democritus and his pupils and that of Dalton and the flourishing schools of chemistry of the last century. The difference lay essentially in the foundation of the theory. It is therefore not surprising to find that chemistry unanimously recognized the atomic theory; adherents to any other theory are no longer to be found. Even if Ostwald stood aside from all his contemporaries at one time, his later conversion to the atomic theory brought all the more support in its favour. The assumption that the whole of matter is made up of atoms is quite generally thought to apply to all bodies and all states of aggregation. Although, on subjective grounds, one is convinced that the atomic theory is true, the wish still remains for some process to be found in which the atomic structure of bodies, as such, would reveal itself to us.