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Expansion \Ex*pan"sion\, n. [L. expansio: cf. F. expansion.]
1. The act of expanding or spreading out; the condition of
being expanded; dilation; enlargement.

2. That which is expanded; expanse; extend surface; as, the
expansion of a sheet or of a lake; the expansion was
formed of metal.

The starred expansion of the skies. --Beattie.

3. Space through which anything is expanded; also, pure
space.

Lost in expansion, void and infinite. --Blackmore.

4. (Economics & Commmerce) an increase in the production of
goods and services over time, and in the volume of
business transactions, generally associated with an
increase in employment and an increase in the money
supply. Opposite of {contraction}.

Syn: economic expansion. [1913 Webster +PJC]

5. (Math.) The developed result of an indicated operation;
as, the expansion of (a + b)^{2} is a^{2} + 2ab + b^{2}.

6. (Steam Engine) The operation of steam in a cylinder after
its communication with the boiler has been cut off, by
which it continues to exert pressure upon the moving
piston.

7. (Nav. Arch.) The enlargement of the ship mathematically
from a model or drawing to the full or building size, in
the process of construction. --Ham. Nav. Encyc.

Note: Expansion is also used adjectively, as in expansion
joint, expansion gear, etc.

8. an enlarged or extended version of something, such as a
writing or discourse; as, the journal article is an
expansion of the lecture she gave.
[PJC]

9. an {expansion joint}. See below. [Colloq. or jargon]
[PJC]

{Expansion curve}, a curve the co["o]rdinates of which show
the relation between the pressure and volume of expanding
gas or vapor; esp. (Steam engine), that part of an
indicator diagram which shows the declining pressure of
the steam as it expands in the cylinder.

{Expansion gear} (Steam Engine). a cut-off gear. See Illust.
of {Link motion}.

{Automatic expansion gear} or {Automatic cut-off}, one that
is regulated by the governor, and varies the supply of
steam to the engine with the demand for power.

{Fixed expansion gear}, or {Fixed cut-off}, one that always
operates at the same fixed point of the stroke.

{Expansion joint}, or {Expansion coupling} (Mech. & Engin.),
a yielding joint or coupling for so uniting parts of a
machine or structure that expansion, as by heat, is
prevented from causing injurious strains; as:
(a) A slide or set of rollers, at the end of bridge truss,
to support it but allow end play.
(b) A telescopic joint in a steam pipe, to permit one part
of the pipe to slide within the other.
(c) A clamp for holding a locomotive frame to the boiler
while allowing lengthwise motion.
(d) a strip of compressible material placed at intervals
between blocks of poured concrete, as in roads or
sidewalks.

{Expansion valve} (Steam Engine), a cut-off valve, to shut
off steam from the cylinder before the end of each stroke.