“_There is this remarkable difference between bodies in a fluid and
bodies in a solid form, namely, that every particle of a fluid is
perfectly independent of every other particle. They do not cohere in
masses, like the particles of a solid, nor do they repel one another,
as is the case with the particles composing a gas. They can mingle
among each other with the least degree of friction, and, when they
press down upon one another by virtue of their own weight, the downward
pressure is communicated in all directions, causing a pressure upwards,
sideways, and in every possible manner. Herein the particles of a fluid
differ from the particles of a solid, even when reduced to the most
impalpable powder; and it is this which constitutes fluidity, namely,
the power of transmitting pressure in every direction, and that, too,
with the least degree of friction. The particles which compose a fluid
must be very much smaller than the finest grain of an impalpable
powder._”—RICHARD GREEN PARKER, A. M.