Chjlp. 1. § 10. OF CLOUDS. 31

It is said again, that nimbi have been observed
to take place without the precurrence of other

'' The author has since espoused a theory of eraporation
which altogether exdudea the abovementioned opinion (and
consequently Dr. Button's also)^ and considers himself in a
considerable degree indebted to it for the origin of the ex*
planation he is about to offer. It will be proper^ therefore, to
state the fundamental propositions of this theory, with such
other parts as appear immediately necessary, referring for
mathematical demonstrations and detail of experiments to the
work itself, which is entitled ^^ Experimental Essays on the
Constitution of mixed Gksiss; o» the Force of Steam or Va-
pour from Water and other Liquids, in different Temperatures,
both in a Torricellian Vacuum and in Air; on Evaporation;
and on the expansion of Elastic Fluids by Heat. By John
Daltou."— rSee Memoirs of the Literary and Philosophical
Society of Manchester, vol. v. part 2. — The propositions are
as foUow:

^1. Whenv two elastic fluids> denoted by A and ^, are
Quxed together, theve is no mutual repulsion amongst their
p(uiicles; that is, the particles of ^ do not repel those of B, aa
they do one another. Consequently, the pressure or whole
wmgbt upon any one particle solely arises from those of its
vwn kind.
