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How does it work? This question has been put to me so often by persons young and old that I have at last decided to answer it in such a manner that a much larger public than that with which I have personal acquaintance may be able to satisfy themselves as to the principles underlying many of the mechanisms met with in everyday life.

In order to include steam, electricity, optics, hydraulics, thermics, light, and a variety of detached mechanisms which cannot be classified under any one of these heads, within the compass of about 450 pages, I have to be content with a comparatively brief treatment of each subject. This brevity has in turn compelled me to deal with principles rather than with detailed descriptions of individual devices—though in several cases recognized types are examined. The reader will look in vain for accounts of the Yerkes telescope, of the latest thing in motor cars, and of the largest locomotive. But he will be put in the way of understanding the essential nature of all telescopes, motors, and steam-engines so far as they are at present developed, which I think may be of greater ultimate profit to the uninitiated.

While careful to avoid puzzling the reader by the use of mysterious phraseology I consider that the parts of a machine should be given their technical names wherever possible. To prevent misconception, many of the diagrams accompanying the letterpress have words as well as letters written on them. This course also obviates the wearisome reference from text to diagram necessitated by the use of solitary letters or figures.

I may add, with regard to the diagrams of this book, that they are purposely somewhat unconventional, not being drawn to scale nor conforming to the canons of professional draughtsmanship. Where advisable, a part of a machine has been exaggerated to show its details. As a rule solid black has been preferred to fine shading in sectional drawings, and all unnecessary lines are omitted. I would here acknowledge my indebtedness to my draughtsman, Mr. Frank Hodgson, for his care and industry in preparing the two hundred or more diagrams for which he was responsible.

Four organs of the body—the eye, the ear, the larynx, and the heart—are noticed in appropriate places. The eye is compared with the camera, the larynx with a reed pipe, the heart with a pump, while the ear fitly opens the chapter on acoustics. The reader who is unacquainted with physiology will thus be enabled to appreciate the better these marvellous devices, far more marvellous, by reason of their absolutely automatic action, than any creation of human hands.

A.W.

Uplands, Stoke Poges, Bucks.

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	13
Chapter II.—THE CONVERSION OF HEAT ENERGY INTO MECHANICAL MOTION.
Reciprocating engines—Double-cylinder engines—The function of the fly-wheel—The cylinder—The slide-valve—The eccentric—"Lap" of the valve: expansion of steam—How the cut-off is managed—Limit of expansive working—Compound engines—Arrangement of expansion engines—Compound locomotives—Reversing gears—"Linking-up"—Piston-valves—Speed governors—Marine-speed governors—The condenser	44
Chapter III.—THE STEAM TURBINE.
How a turbine works—The De Laval turbine—The Parsons turbine—Description of the Parsons turbine—The expansive action of steam in a Parsons turbine—Balancing the thrust—Advantages of the marine turbine	74
Chapter IV.—THE INTERNAL-COMBUSTION ENGINE.
The meaning of the term—Action of the internal-combustion engine—The motor car—The starting-handle—The engine—The carburetter—Ignition of the charge—Advancing the spark—Governing the engine—The clutch—The gear-box—The compensating gear—The silencer—The brakes—Speed of cars	87
Chapter V.—ELECTRICAL APPARATUS.
What is electricity?—Forms of electricity—Magnetism—The permanent magnet—Lines of force—Electro-magnets—The electric bell—The induction coil—The condenser—Transformation of current—Uses of the induction coil	112
Chapter VI.—THE ELECTRIC TELEGRAPH.
Needle instruments—Influence of current on the magnetic needle—Method of reversing the current—Sounding instruments—Telegraphic relays—Recording telegraphs—High-speed telegraphy	127
Chapter VII.—WIRELESS TELEGRAPHY.
The transmitting apparatus—The receiving apparatus—Syntonic transmission—The advance of wireless telegraphy	137
Chapter VIII.—THE TELEPHONE.
The Bell telephone—The Edison transmitter—The granular carbon transmitter—General arrangement of a telephone circuit—Double-line circuits—Telephone exchanges—Submarine telephony	147
Chapter IX.—DYNAMOS AND ELECTRIC MOTORS.
A simple dynamo--Continuous-current dynamos--Multipolar dynamos--Exciting the field magnets--Alternating current dynamos--The transmission of power--The electric motor--Electric lighting--The incandescent lamp--Arc lamps--"Series" and "parallel" arrangement of lamps--Current for electric lamps--Electroplating	159
Chapter X.—RAILWAY BRAKES.
The Vacuum Automatic brake—The Westinghouse air-brake	187
Chapter XI.—RAILWAY SIGNALLING.
The block system—Position of signals—Interlocking the signals—Locking gear—Points—Points and signals in combination—Working the block system—Series of signalling operations—Single line signals—The train staff—Train staff and ticket—Electric train staff system—Interlocking—Signalling operations—Power signalling—Pneumatic signalling—Automatic signalling	200
Chapter XII.—OPTICS.
Lenses—The image cast by a convex lens—Focus—Relative position of object and lens—Correction of lenses for colour—Spherical aberration—Distortion of image—The human eye—The use of spectacles—The blind spot	230
Chapter XIII.—THE MICROSCOPE, THE TELESCOPE, AND THE MAGIC-LANTERN.
The simple microscope—Use of the simple microscope in the telescope—The terrestrial telescope—The Galilean telescope—The prismatic telescope—The reflecting telescope—The parabolic mirror—The compound microscope—The magic-lantern—The bioscope—The plane mirror	253
Chapter XIV.—SOUND AND MUSICAL INSTRUMENTS.
Nature of sound—The ear—Musical instruments—The vibration of strings—The sounding-board and the frame of a piano—The strings—The striking mechanism—The quality of a note	270
Chapter XV.—WIND INSTRUMENTS.
Longitudinal vibration—Columns of air—Resonance of columns of air—Length and tone—The open pipe—The overtones of an open pipe—Where overtones are used—The arrangement of the pipes and pedals—Separate sound-boards—Varieties of stops—Tuning pipes and reeds—The bellows—Electric and pneumatic actions—The largest organ in the world—Human reeds	287
Chapter XVI.—TALKING-MACHINES.
The phonograph—The recorder—The reproducer—The gramophone—The making of records—Cylinder records—Gramophone records	310
Chapter XVII.—WHY THE WIND BLOWS.
Why the wind blows—Land and sea breezes—Light air and moisture—The barometer—The column barometer—The wheel barometer—A very simple barometer—The aneroid barometer—Barometers and weather—The diving-bell—The diving-dress—Air-pumps—Pneumatic tyres—The air-gun—The self-closing door-stop—The action of wind on oblique surfaces—The balloon—The flying-machine	322
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