The scruples of physicists ought to have been removed on the memorable occasion when Professor Van t'Hoff demonstrated that solution can operate reversibly by reason of the phenomena of osmosis.

But the experiment can only succeed in very rare cases; and, on the other hand, Professor Van t'Hoff was naturally led to another very bold conception.

He regarded the molecule of the dissolved body as a gaseous one, and assimilated solution, not as had hitherto been the rule, to fusion, but to a kind of vaporization.

Naturally his ideas were not immediately accepted by the scholars most closely identified with the classic tradition.

It may perhaps not be without use to examine here the principles of Professor Van t'Hoff's theory.
Sec.2.