experiment. Bell, the inventor of the telephone, transmits speech by a beam of light

387 XXVII. BESSEMER, CREATOR OF CHEAP STEEL. NOBEL, INVENTOR OF NEW EXPLOSIVES
Bessemer a man of golden ignorances. His boldness and versatility. The story of his steel process told by himself. Nobel’s heroic courage in failure and adversity. His triumph at last. Turns an accidental hint to great profit. Inventors to-day organized for attacks of new breadth and audacity 401 XXVIII. COMPRESSED AIR
An aid to the miner, quarryman and sculptor. An actuator for pumps. Engraves glass and cleans castings. Dust and dirt removed by air exhaustion. Westinghouse air-brakes and signals 417 XXIX. CONCRETE AND ITS REINFORCEMENT
Pouring and ramming are easier and cheaper than cutting and carving. Concrete for dwellings ensures comfort and safety from fire. Strengthened with steel it builds warehouses, factories and bridges of new excellence 429 XXX. MOTIVE POWERS PRODUCED WITH NEW ECONOMY
Improvements in steam practice. Mechanical draft. Automatic stokers. Better boilers. Superheaters. Economical condensers. Steam turbines on land and sea 446 XXXI. MOTIVE POWERS, CONTINUED. HEATING SERVICES
Producer gas. Mond gas. Gas engines. Steam and gas engines compared. Diesel engine best heat motor of all. Gasoline motors. Alcohol engines. Steam and gas motors united. Heat and power production together. District steam heating. Isolated plants. Electric traction. Gas for a service of heat, light and power 457 XXXII. A FEW SOCIAL ASPECTS OF INVENTION
Why cities gain at the expense of the country. The factory system. Small shops multiplied. Subdivided labor has passed due bounds and is being modified. Tendencies against centralization and monopoly. Dwellings united for new services. Self-contained houses warmed from a center. The literature of invention and discovery as purveyed in public libraries 478   INDEX 489

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LIST OF ILLUSTRATIONS

Professor Alexander Graham Bell	Frontispiece
Bell Homestead, Brantford, Ontario	facing 2
Lens of ice focussing a sunbeam	5
Rubber strip suspended plank-wise and joist-wise	7
Board doubled breadthwise and edgewise	7
Telegraph poles under compression. Wires under tension	8
Rubber cylinder, flattened by compression, lengthened by tension	9
Rubber joist compressed along top, extended along bottom	10
Girder cut from joist	10
Rubber I-beam suspended flatwise and edgewise	10
Girder contours simple, built up, in locomotive draw-bars	11
Steel ore car	12
Bulb angle column, New York Subway	12
Strap rail and stringer, Mohawk & Hudson R. R., 1830	13
Plimmon H. Dudley	facing 14
Dudley rails	16
Steel cross-ties and rails	17
King-post truss	18
Frames of four sides	19
Cross-section Arctic ship “Roosevelt”	20
Pair of compasses stretch a rubber strip	20
Queen-post truss	21
Upper part of roof truss, Interborough Power House, New York	21
Two queen-post trusses from a bridge	22
Palladio trusses	22
Burr Bridge, Waterford, N. Y.	23
Howe and Pratt trusses	24
Baltimore truss	25
Whipple Bridge	25
Simple cantilevers	26
Victoria Bridge, Montreal, original form	27
Victoria Bridge, Montreal, present form	28
Cantilever Bridge, near Quebec	29
Kentucky River Cantilever Bridge	30
Arch Bridge, Niagara Falls	31
Bowstring Bridge, Philadelphia	32
Williamsburg Bridge, New York City	33
Continuous Girder Bridge, Lachine, near Montreal	34
Rubber strip supported at 4 points, and at 2 points	34
Plate girder bridge	35
Lattice girder bridge, showing rivets	36
Bookshelf laden and unladen, showing camber	36
Pin connecting parts of bridge	37
Bridge rollers in section and in plan	38
Girder sections in various forms	39
Rubber cylinders solid and hollow compared in sag	40
Handle bar of bicycle in steel tubing	40
A sulky in steel tubing	41
Pneumatic hammer in steel tubing	41
Fishing rod in steel