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. CONTENTS. 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.