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]