less degree, required aid and reciprocated it. Indeed,
it needs but to throw aside these, and contemplate the mixed character
of surrounding phenomena, to at once see that these notions of division
and succession in the kinds of knowledge are none of them actually true,
but are simple scientific fictions: good, if regarded merely as aids to
study; bad, if regarded as representing realities in Nature. Consider
them critically, and no facts whatever are presented to our senses
uncombined with other facts--no facts whatever but are in some degree
disguised by accompanying facts: disguised in such a manner that all
must be partially understood before any one can be understood. If it be
said, as by M. Comte, that gravitating force should be treated of before
other forces, seeing that all things are subject to it, it may on like
grounds be said that heat should be first dealt with; seeing that
thermal forces are everywhere in action; that the ability of any portion
of matter to manifest visible gravitative phenomena depends on its state
of aggregation, which is determined by heat; that only by the aid of
thermology can we explain those apparent exceptions to the gravitating
tendency which are presented by steam and smoke, and so establish its
universality, and that, indeed, the very existence of the solar system
in a solid form is just as much a question of heat as it is one of
gravitation.

Take other cases:--All phenomena recognised by the eyes, through which
only are the data of exact science ascertainable, are complicated with
optical phenomena; and cannot be exhaustively known until optical
principles are known. The burning of a candle cannot be explained
without involving chemistry, mechanics, thermology. Every wind that
blows is determined by influences partly solar, partly lunar, partly
hygrometric; and implies considerations of fluid equilibrium and
physical geography. The direction, dip, and variations of the magnetic
needle, are facts half terrestrial, half celestial--are caused by
earthly forces which have cycles of change corresponding with
astronomical periods. The flowing of the gulf-stream and the annual
migration of icebergs towards the equator, depending as they do on the
balancing of the centripetal and centrifugal forces acting on the ocean,
involve in their explanation the Earth's rotation and spheroidal form,
the laws of hydrostatics, the relative densities of cold and warm water,
and the doctrines of ev