original force and any retarding agent, is its _proximate_ cause.
When the original cause is permanent as well as the effect (e.g. Suppose
a continuance of the iron's exposure to moist air), we get a progressive
series of effects arising from the cause's accumulating influence; and
the sum of these effects amounts exactly to what a number of
successively introduced similar causes would have produced. Such cases
fall under the head of Composition of Causes, with this peculiarity,
that, as the causes (to regard them as plural) do not come into play all
at once, the effect at each instant is the sum of the effects only of
the then acting causes, and the result will appear as an ascending
series. Each addition in such case takes place according to a fixed law
(equal quantities in equal times); and therefore it can be computed
deductively. Even when, as is sometimes the case, a cause is at once
permanent and progressive (as, e.g. the sun, by its position becoming
more vertical, increases the heat in summer) so that the quantities
added are unequal, the effect is still progressive, resulting from its
cause's continuance and progressiveness combined.

In _all_ cases whatever of progressive effects, the succession not
merely between the cause and the effect, but also between the first and
latter stages of the effect, is uniform. Hence, from the invariable
sequence of two terms (e.g. Spring and Summer) in a series going through
any continued and uniform process of variation, we do not presume that
one is the cause and the others the effect, but rather that the whole
series is an effect.

CHAPTER XVI.

EMPIRICAL LAWS.

Empirical laws are derivative laws, of which the derivation is not
known. They are observed uniformities, which we compare with the result
of any deduction to verify it; but of which the _why_, and also the
limits, are unrevealed, through their being, though resolvable, not yet
resolved into the simpler laws. They depend usually, not solely on the
ultimate laws into which they are resolvable; but on those, together
with an ultimate fact, viz. the mode of coexistence of some of the
component elements of the universe. Hence their untrustworthiness for
scientific purposes; for, till they have been resolved (and then a
derivative law ceases to be empirical), we cannot know whether they
result from the different effects of one cause, or from effects of
different causes; that is, whether they depend on laws,