eralization= states a broad principle, or a general truth, derived
from examination of a considerable number of individual facts. This
synthetic exposition is not the same as argumentative generalization,
which supports a general contention by citing instances in proof.
Observe how Holmes begins with one fact, and by adding another and
another reaches a complete whole. This is one of the most effective
devices in the public speaker's repertory.

Take a hollow cylinder, the bottom closed while the top remains
open, and pour in water to the height of a few inches. Next
cover the water with a flat plate or piston, which fits the
interior of the cylinder perfectly; then apply heat to the
water, and we shall witness the following phenomena. After the
lapse of some minutes the water will begin to boil, and the
steam accumulating at the upper surface will make room for
itself by raising the piston slightly. As the boiling continues,
more and more steam will be formed, and raise the piston higher
and higher, till all the water is boiled away, and nothing but
steam is left in the cylinder. Now this machine, consisting of
cylinder, piston, water, and fire, is the steam-engine in its
most elementary form. For a steam-engine may be defined as an
apparatus for doing work by means of heat applied to water; and
since raising such a weight as the piston is a form of doing
work, this apparatus, clumsy and inconvenient though it may be,
answers the definition precisely.[17]

=Reference to Experience= is one of the most vital principles in
exposition--as in every other form of discourse.

"Reference to experience, as here used, means reference to the known.
The known is that which the listener has seen, heard, read, felt,
believed or done, and which still exists in his consciousness--his stock
of knowledge. It embraces all those thoughts, feelings and happenings
which are to him real. Reference to Experience, then, means _coming into
the listener's life_.[18]

The vast results obtained by science are won by no mystical
faculties, by no mental processes, other than those which are
practised by every one of us in the humblest and meanest affairs
of life. A detective policeman discovers a burglar from the
marks made by his shoe, by a mental process identical with that
by which Cuvier restored the extinct animals of Montmartre from
fragments o