ubbles of air_ which are by any means conveyed under the surface
of the _water_; or a drop of common _Sallet Oyl_ swimming upon water. In
all which, and many more examples of this kind that might be enumerated,
the _incongruity_ of two _fluids_ is easily discernable. And as for the
_Congruity_ or _Incongruity_ of Liquids, with several kinds of _firm_
Bodies, they have long since been taken notice of, and called by the Names
of _Driness_ and _Moisture_ (though these two names are not comprehensive
enough, being commonly used to signifie only the adhering or not adhering
of _water_ to some other _solid Bodies_) of this kind we may observe that
_water_ will more readily _wet some woods_ then _others_; and that _water_,
let fall upon a _Feather_, the whiter side of a _Colwort_, and some other
leaves, or upon almost any _dusty_, _unctuous_, or _resinous_ superficies,
will not _at all adhere_ to them, but easily _tumble off_ from them, like a
solid _Bowl_; whereas, if dropt upon _Linnen_, _Paper_, _Clay_, _green
Wood_, &c. it will not be taken off, without leaving some part of it behind
_adhering_ to them. So _Quick-silver_, which will very _hardly_ be brought
to _stick_ to any _vegetable body_, will _readily adhere_ to, and _mingle_
with, several clean _metalline bodies_.

And that we may the better finde what the _cause_ of _Congruity_ and
_Incongruity_ in bodies is, it will be requisite to consider, First, what
is the _cause_ of _fluidness_; And this, _I conceive_, to be nothing else
but a certain _pulse_ or _shake_ of _heat_; for Heat being nothing else but
a very _brisk_ and _vehement agitation_ of the parts of a body (as I have
elswhere made _probable_) the parts of a body are thereby made so _loose_
from one another, that they easily _move any way_, and become _fluid_. That
I may explain this a little by a gross Similitude, let us suppose a dish of
sand set upon some body that is very much _agitated_, and shaken with some
_quick_ and _strong vibrating motion_, as on a _Milstone_ turn'd round upon
the under stone very violently whilst it is empty; or on a very stiff
_Drum_-head, which is vehemently or very nimbly beaten with the Drumsticks.
By this means, the sand in the dish, which before lay like a _dull_ and
unactive body, becomes a perfect _fluid_; and ye can no sooner make a
_hole_ in it with your finger, but it is immediately _filled up again_, and
the upper surface of it _levell'd_. Nor can you _bury_ a _light body_