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Chapter XVIII.--HYDRAULIC MACHINERY.

The siphon--The bucket pump--The force-pump--The most marvellous
pump--The blood channels--The course of the blood--The
hydraulic press--Household water-supply fittings--The
ball-cock--The water-meter--Water-supply systems--The household
filter--Gas traps--Water engines--The cream separator--The
"hydro" 350

Chapter XIX.--HEATING AND LIGHTING.

The hot-water supply--The tank system--The cylinder system--How
a lamp works--Gas and gasworks--Automatic stoking--A
gas governor--The gas meter--Incandescent gas lighting 386

Chapter XX.--VARIOUS MECHANISMS.

CLOCKS AND WATCHES:--A short history of timepieces--The construction
of timepieces--The driving power--The escapement--Compensating
pendulums--The spring balance--The cylinder
escapement--The lever escapement--Compensated balance-wheels--Keyless
winding mechanism for watches--The hour hand
train. LOCKS:--The Chubb lock--The Yale lock. THE CYCLE:--The
gearing of a cycle--The free wheel--The change-speed gear.
AGRICULTURAL MACHINES:--The threshing-machine--Mowing-machines.
SOME NATURAL PHENOMENA:--Why sun-heat varies
in intensity--The tides--Why high tide varies daily 410

HOW IT WORKS.

Chapter I.

THE STEAM-ENGINE.

What is steam?--The mechanical energy of steam--The boiler--The
circulation of water in a boiler--The enclosed furnace--The
multitubular boiler--Fire-tube boilers--Other types of
boilers--Aids to combustion--Boiler fittings--The safety-valve--The
water-gauge--The steam-gauge--The water supply to a boiler.

WHAT IS STEAM?

If ice be heated above 32 deg. Fahrenheit, its molecules lose their
cohesion, and move freely round one another--the ice is turned into
water. Heat water above 212 deg. Fahrenheit, and the molecules exhibit a
violent mutual repulsion, and, like dormant bees revived by spring
sunshine, separate and dart to and fro. If confined in an air-tight
vessel, the molecules have their flights curtailed, and beat more and
more violently against their prison walls, so that every square inch of
the vessel is subjected to a rising pressure. We may compare the action
of the steam molecules to that of bullets fired from a machine-gun at a
plate mounted on a spring. The faster the bullets came, the greater
would be the continuous compression of the spring.

THE MECHANICAL ENERGY OF STEAM.

If steam is let into one end of a cylinder