ILLUSTRATIONS

FACING

PAGE

The Great Scarlet Solar Prominences, Which are Such a Notable Feature of the Solar Phenomena, are Immense Outbursts of Flaming Hydrogen Rising Sometimes to a Height of 500,000 Miles Coloured Frontispiece

Laplace 10

Professor J. C. Adams 10

Photo: Royal Astronomical Society.

Professor Eddington of Cambridge University 10

Photo: Elliot & Fry, Ltd.

The Planets, Showing their Relative Distances and Dimensions 11

The Milky Way 14

Photo: Harvard College Observatory.

The Moon Entering the Shadow Cast by the Earth 14

The Great Nebula in Andromeda, Messier 31 15

From a photograph taken at the Yerkes Observatory.

Diagram Showing the Main Layers of the Sun 18

Solar Prominences Seen at Total Solar Eclipse, May 29, 1919. Taken at Sobral, Brazil 18

Photo: Royal Observatory, Greenwich.

The Visible Surface of the Sun 19

Photo: Mount Wilson Observatory.

The Sun Photographed in the Light of Glowing Hydrogen 19

Photo: Mount Wilson Observatory.

The Aurora Borealis (Coloured Illustration) 20

Reproduced from The Forces of Nature (Messrs. Macmillan)

The Great Sun-Spot of July 17, 1905 22

Yerkes Observatory.

Solar Prominences 22

From photographs taken at the Yerkes Observatory.

Mars, October 5, 1909 23

Photo: Mount Wilson Observatory.

Jupiter 23

Saturn, November 19, 1911 23

Photo: Professor E. E. Barnard, Yerkes Observatory.

The Spectroscope, an Instrument for Analysing Light; it Provides Means for Identifying Substances (Coloured Illustration) 24

The Moon 28

Mars 29

Drawings by Professor Percival Lowell.

The Moon, at Nine and Three Quarter Days 29

A Map of the Chief Plains and Craters of the Moon 32

A Diagram of a Stream of Meteors Showing the Earth Passing Through Them 32

Comet, September 29, 1908 33

Photo: Royal Observatory, Greenwich.

Comet, October 3, 1908 33

Photo: Royal Observatory, Greenwich.

Typical Spectra 36

Photo: Harvard College Observatory.

A Nebular Region South of Zeta Orionis 37

Photo: Mount Wilson Observatory.

Star Cluster in Hercules 37

Photo: Astrophysical Observatory, Victoria, British Columbia.

The Great Nebula in Orion 40

Photo: Yerkes Observatory.

Giant Spiral Nebula, March 23, 1914 41

Photo: Lick Observatory.

A Spiral Nebula Seen Edge-on 44

Photo: Mount Wilson Observatory.

100-Inch Telescope, Mount Wilson 45

Photo: H. J. Shepstone.

The Yerkes 40-Inch Refractor 48

The Double-Slide Plate-Holder on Yerkes 40-Inch Refracting Telescope 49

Photo: H. J. Shepstone.

Modern Direct-Reading Spectroscope 49

By A. Hilger, Ltd.

Charles Darwin 56

Photo: Rischgitz Collection.

Lord Kelvin 56

Photo: Rischgitz Collection.

A Giant Spiral Nebula 57

Photo: Lick Observatory.

Meteorite Which Fell Near Scarborough and is now to be Seen in the Natural History Museum 57

Photo: Natural History Museum.

A Limestone Canyon 60

Reproduced from the Smithsonian Report, 1915.

Geological Tree of Animals 61

Diagram of Amœba 61

A Piece of a Reef-Building Coral, Built up by a Large Colony of Small Sea-Anemone-Like Polyps, Each of which Forms from the Salts of the Sea a Skeleton or Shell of Lime 64

From the Smithsonian Report, 1917.

A Group of Chalk-Forming Animals, or Foraminifera, Each about the Size of a Very Small Pin's Head 65

Photo: J. J. Ward, F.E.S.

A Common Foraminifer (Polystomella) Showing the Shell in the Centre and the Outflowing Network of Living Matter, Along which Granules are Continually Travelling, and by which Food Particles are Entangled and Drawn in 65

Reproduced by permission of the Natural History Museum (after Max Schultze).

A Plant-Like Animal, or Zoophyte, Called Obelia 68

Photo: J. J. Ward, F.E.S.

Trypanosoma Gambiense 69

Reproduced by permission of The Quart. Journ. Mic. Sci.

Volvox 69

Proterospongia 69

Green Hydra 72

Photo: J. J. Ward, F.E.S.

Diagram Illustrating the Beginning of Individual Life 72

Earthworm 72

Photo: J. J. Ward, F.E.S.

Glass Model of a Sea-Anemone 72

Reproduced from the Smithsonian Report, 1917.

This Drawing Shows the Evolution of the Brain from Fish to Man 73

Okapi and Giraffe (Coloured Illustration) 74

Diagram of a Simple Reflex Arc in a Backboneless Animal Like an Earthworm 76

The Yucca Moth 76

Photo: British Museum (Natural History).

Inclined Plane of Animal Behaviour 76

Venus' Fly-Trap 77

Photo: J. J. Ward, F.E.S.

A Spider Sunning Her Eggs 77

Reproduced by permission from The Wonders of Instinct by J. H. Fabre.

The Hoatzin Inhabits British Guiana 82

Peripatus 83

Photograph, from the British Museum (Natural History), of a drawing by Mr. E. Wilson.

Rock Kangaroo Carrying its Young in a Pouch 83

Photo: W. S. Berridge, F.Z.S.

Professor Thomas Henry Huxley (1825-95) 86

Photo: Rischgitz.

Baron Cuvier, 1769-1832 86

An Illustration Showing Various Methods of Flying and Swooping 87

Animals of the Cambrian Period 90

From Knipe's Nebula to Man.

A Trilobite 90

Photo: J. J. Ward, F.E.S.

The Gambian Mud-Fish, Protopterus 91

Photo: British Museum (Natural History).

The Archæopteryx 91

After William Leche of Stockholm.

Wing of a Bird, Showing the Arrangement of the Feathers 91

Pictorial Representation of Strata of the Earth's Crust, with Suggestions of Characteristic Fossils (Coloured Illustration) 92

Fossil of a Pterodactyl or Extinct Flying Dragon 94

Photo: British Museum (Natural History).

Pariasaurus: An Extinct Vegetarian Triassic Reptile 94

From Knipe's Nebula to Man.

Triceratops: A Huge Extinct Reptile 95

From Knipe's Nebula to Man.

The Duckmole or Duck-Billed Platypus of Australia 95

Photo: Daily Mail.

Skeleton of an Extinct Flightless Toothed Bird, Hesperornis 100

After Marsh.

Six Stages in the Evolution of the Horse, Showing Gradual Increase in Size 101

After Lull and Matthew.

Diagram Showing Seven Stages in the Evolution of the Fore-Limbs and Hind-Limbs of the Ancestors of the Modern Horse, Beginning with the Earliest Known Predecessors of the Horse and Culminating with the Horse of To-Day 104

After Marsh and Lull.

What is Meant by Homology? Essential Similarity of Architecture, though the Appearances May be Very Different 105

An Eight-Armed Cuttlefish or Octopus Attacking a Small Crab 116

A Common Starfish, which has Lost Three Arms and is Regrowing Them 116

After Professor W. C. McIntosh.

The Paper Nautilus (Argonauta), an Animal of the Open Sea 117

Photo: J. J. Ward, F.E.S.

A Photograph Showing a Starfish (Asterias Forreri) which has Captured a Large Fish 117

Ten-Armed Cuttlefish or Squid in the Act of Capturing a Fish 118

Greenland Whale 118

Minute Transparent Early Stage of a Sea-Cucumber 119

An Intricate Colony of Open-Sea Animals (Physophora Hydrostatica) Related to the Portuguese Man-of-War 119

Photo: British Museum (Natural History).

A Scene in the Great Depths 119

Sea-Horse in Sargasso Weed 120

Large Marine Lampreys (Petromyzon Marinus) 120

The Deep-Sea Fish Chiasmodon Niger 120

Deep-Sea Fishes 120

Flinty Skeleton of Venus' Flower Basket (Euplectella), a Japanese Deep-Sea Sponge 121

Egg Depository of Semotilus Atromaculatus 121

The Bitterling (Rhodeus Amarus) 124

Woolly Opossum Carrying her Family 124

Photo: W. S. Berridge.

Surinam Toad (Pipa Americana) with Young Ones Hatching out of Little Pockets on her Back 125

Storm Petrel or Mother Carey's Chicken (Procellaria Pelagica) 125

Albatross: A Characteristic Pelagic Bird of the Southern Sea 128

The Praying Mantis (Mantis Religiosa) 138

Protective Coloration: A Winter Scene in North Scandinavia 138

The Variable Monitor (Varanus) 139

Photo: A. A. White.

Banded Krait: A Very Poisonous Snake with Alternating Yellow and Dark Bands 140

Photo: W. S. Berridge, F.Z.S.

The Warty Chameleon 140

Photos: W. S. Berridge, F.Z.S.

Seasonal Colour-Change: Summer Scene in North Scandinavia 141

Protective Resemblance 142

Photo: J. J. Ward, F.E.S.

When Only a Few Days Old, Young Bittern Begin to Strike the Same Attitude as their Parents, Thrusting their Bills upwards and Drawing their Bodies up so that they Resemble a Bunch of Reeds 143

Protective Coloration or Camouflaging, Giving Animals a Garment of Invisibility (Coloured Illustration) 144

Another Example of Protective Coloration (Coloured Illustration) 144

Dead-Leaf Butterfly (Kallima Inachis) from India 146

Protective Resemblance between a Small Spider (to the left) and an Ant (to the right) 146

The Wasp Beetle, which, when Moving amongst the Branches, Gives a Wasp-Like Impression 147

Photo: J. J. Ward, F.E.S.

Hermit-Crab with Partner Sea-Anemones 147

Cuckoo-Spit 147

Photo: G. P. Duffus.

Chimpanzee, Sitting 156

Photo: New York Zoological Park.

Chimpanzee, Illustrating Walking Powers 156

Photo: New York Zoological Park.

Surface View of the Brains of Man and Chimpanzee 157

Side-View of Chimpanzee's Head 157

Photo: New York Zoological Park.

Profile View of Head of Pithecanthropus, the Java Ape-Man, Reconstructed from the Skull-Cap 157

After a model by J. H. McGregor.

The Flipper of a Whale and the Hand of a Man 157

The Gorilla, Inhabiting the Forest Tract of the Gaboon in Africa (Coloured Illustration) 158

"Darwin's Point" on Human Ear 160

Professor Sir Arthur Keith, M.D., LL.D., F.R.S. 161

Photo: J. Russell & Sons.

Skeletons of the Gibbon, Orang, Chimpanzee, Gorilla, Man 161

After T. H. Huxley (by permission of Messrs. Macmillan).

Side-View of Skull of Man and Gorilla 164

The Skull and Brain-Case of Pithecanthropus, the Java Ape-Man, as Restored by J. H. McGregor from the Scanty Remains 164

Suggested Genealogical Tree of Man and Anthropoid Apes 165

The Gibbon is Lower than the Other Apes as Regards its Skull and Dentition, but it is highly Specialized in the Adaptation of its Limbs to Arboreal Life 166

Photo: New York Zoological Park.

The Orang Has a High Rounded Skull and a Long Face 166

Photo: New York Zoological Park.

Comparisons of the Skeletons of Horse and Man 167

Photo: British Museum (Natural History).

A Reconstruction of the Java Man (Coloured Illustration) 168

Profile View of the Head of Pithecanthropus, the Java Ape-Man—an Early Offshoot from the Main Line of Man's Ascent 170

After a model by J. H. McGregor.

Piltdown Skull 170

From the reconstruction by J. H. McGregor.

Sand-Pit at Mauer, near Heidelberg: Discovery Site of the Jaw of Heidelberg Man 171

Reproduced by permission from Osborn's Men of the Old Stone Age.

Paintings on the Roof of the Altamira Cave in Northern Spain, Showing a Bison and a Galloping Boar (Coloured Illustration) 172

Piltdown Man, Preceding Neanderthal Man, Perhaps 100,000 to 150,000 Years Ago 174

After the restoration modelled by J. H. McGregor.

The Neanderthal Man of La Chapelle-aux-Saints 175

After the restoration modelled by J. H. McGregor.

Restoration by A. Forestier of the Rhodesian Man whose Skull was Discovered in 1921 176-177

Side View of a Prehistoric Human Skull Discovered in 1921 in Broken Hill Cave, Northern Rhodesia 178

Photo: British Museum (Natural History).

A Cromagnon Man or Cromagnard, Representative of a Strong Artistic Race Living in the South of France in the Upper Pleistocene, Perhaps 25,000 Years Ago 178

After the restoration modelled by J. H. McGregor.

Photograph Showing a Narrow Passage in the Cavern of Font-de-Gaume on the Beune 179

Reproduced by permission from Osborn's Men of the Old Stone Age.

A Mammoth Drawn on the Wall of the Font-de-Gaume Cavern 179

A Grazing Bison, Delicately and Carefully Drawn, Engraved on a Wall of the Altamira Cave, Northern Spain 179

Photograph of a Median Section through the Shell of the Pearly Nautilus 186

Photograph of the Entire Shell of the Pearly Nautilus 186

Nautilus 186

Shoebill 187

Photo: W. S. Berridge.

The Walking-Fish or Mud-Skipper (Periophthalmus), Common at the Mouths of Rivers in Tropical Africa, Asia, and North-West Australia 190

The Australian More-Pork or Podargus 190

Photo: The Times.

Pelican's Bill, Adapted for Catching and Storing Fishes 191

Spoonbill's Bill, Adapted for Sifting the Mud and Catching the Small Animals, e.g. Fishes, Crustaceans, Insect Larvæ, which Live there 191

Avocet's Bill, Adapted for a Curious Sideways Scooping in the Shore-Pools and Catching Small Animals 191

Hornbill's Bill, Adapted for Excavating a Nest in a Tree, and Also for Seizing and Breaking Diverse Forms of Food, from Mammals to Tortoises, from Roots to Fruits 191

Falcon's Bill, Adapted for Seizing, Killing, and Tearing Small Mammals and Birds 191

Puffin's Bill, Adapted for Catching Small Fishes near the Surface of the Sea, and for Holding them when Caught and Carrying them to the Nest 191

Life-History of a Frog 192

Hind-Leg of Whirligig Beetle which has Become Beautifully Modified for Aquatic Locomotion 192

Photo: J. J. Ward, F.E.S.

The Big Robber-Crab (Birgus Latro), that Climbs the Coconut Palm and Breaks off the Nuts 193

Early Life-History of the Salmon 196

The Salmon Leaping at the Fall is a Most Fascinating Spectacle 197

Diagram of the Life-History of the Common Eel (Anguilla Vulgaris) 200

Cassowary 201

Photo: Gambier Bolton.

The Kiwi, Another Flightless Bird, of Remarkable Appearance, Habits, and Structure 201

Photo: Gambier Bolton.

The Australian Frilled Lizard, which is at Present Trying to Become a Biped 202

A Carpet of Gossamer 202

The Water Spider 203

Jackdaw Balancing on a Gatepost 208

Photo: O. J. Wilkinson.

Two Opossums Feigning Death 208

From Ingersoll's The Wit of the Wild.

Male of Three-Spined Stickleback, Making a Nest of Water-Weed, Glued Together by Viscid Threads Secreted from the Kidneys at the Breeding Season 209

A Female Stickleback Enters the Nest which the Male has Made, Lays the Eggs Inside, and then Departs 209

Homing Pigeon 212

Photo: Imperial War Museum.

Carrier Pigeon 212

Photo: Imperial War Museum.

Yellow-Crowned Penguin 213

Photo: James's Press Agency.

Penguins are "A Peculiar People" 213

Photo: Cagcombe & Co.

Harpy-Eagle 216

Photo: W. S. Berridge.

The Dingo or Wild Dog of Australia, Perhaps an Indigenous Wild Species, Perhaps a Domesticated Dog that has Gone Wild or Feral 216

Photo: W. S. Berridge, F.Z.S.

Woodpecker Hammering at a Cotton-Reel, Attached to a Tree 217

The Beaver 220

The Thrush at its Anvil 221

Photo: F. R. Hinkins & Son.

Alsatian Wolf-Dog 226

Photo: Lafayette.

The Polar Bear of the Far North 227

Photo: W. S. Berridge.

An Alligator "Yawning" in Expectation of Food 227

From the Smithsonian Report, 1914.

Baby Orang 232

Photo: W. P. Dando.

Orang-Utan 232

Photo: Gambier Bolton.

Chimpanzee 233

Photo: James's Press Agency.

Baby Orang-Utan 233

Photo: James's Press Agency.

Orang-Utan 233

Photo: James's Press Agency.

Baby Chimpanzees 233

Photo: James's Press Agency.

Chimpanzee 238

Photo: W. P. Dando.

Young Cheetahs, or Hunting Leopards 238

Photo: W. S. Berridge.

Common Otter 239

Photo: C. Reid.

Sir Ernest Rutherford 246

Photo: Elliott & Fry.

J. Clerk-Maxwell 246

Photo: Rischgitz Collection.

Sir William Crookes 247

Photo: Ernest H. Mills.

Professor Sir W. H. Bragg 247

Photo: Photo Press.

Comparative Sizes of Molecules 250

Inconceivable Numbers and Inconceivably Small Particles 250

What is a Million? 250

The Brownian Movement 251

A Soap Bubble (Coloured Illustration) 252

Reproduced from The Forces of Nature (Messrs. Macmillan).

Detecting a Small Quantity of Matter 254

From Scientific Ideas of To-day.

This X-Ray Photograph is that of a Hand of a Soldier Wounded in the Great War 254

Reproduced by permission of X-Rays Ltd.

An X-Ray Photograph of a Golf Ball, Revealing an Imperfect Core 254

Photo: National Physical Laboratory.

A Wonderful X-Ray Photograph 255

Reproduced by permission of X-Rays Ltd.

Electric Discharge in a Vacuum Tube 258

The Relative Sizes of Atoms and Electrons 258

Electrons Streaming from the Sun to the Earth 259

Professor Sir J. J. Thomson 262

Electrons Produced by Passage of X-Rays through Air 262

From the Smithsonian Report, 1915.

Magnetic Deflection of Radium Rays 263

Professor R. A. Millikan's Apparatus for Counting Electrons 263

Reproduced by permission of Scientific American.

Making the Invisible Visible 266

The Theory of Electrons 267

Arrangements of Atoms in a Diamond 267

Disintegration of Atoms 270

Silk Tassel Electrified 270

Reproduced by permission from The Interpretation of Radium (John Murray).

Silk Tassel Discharged by the Rays from Radium 270

A Huge Electric Spark 271

Electrical Attraction between Common Objects 271

From Scientific Ideas of To-day.

An Electric Spark 274

Photo: Leadbeater.

An Ether Disturbance around an Electron Current 275

From Scientific Ideas of To-day.

Lightning 278

Photo: H. J. Shepstone.

Light Waves 279

The Magnetic Circuit of an Electric Current 279

The Magnet 279

Rotating Disc of Sir Isaac Newton for Mixing Colours (Coloured Illustration) 280

Wave Shapes 282

The Power of a Magnet 282

The Speed of Light 283

Photo: The Locomotive Publishing Co., Ltd.

Rotating Disc of Sir Isaac Newton for Mixing Colours 283

Niagara Falls 286

Transformation of Energy 287

Photo: Stephen Cribb.

"Boiling" a Kettle on Ice 287

Photo: Underwood & Underwood.

The Cause of Tides 290

The Aegir on the Trent 290

Photo: G. Brocklehurst.

A Big Spring Tide, the Aegir on the Trent 291

Photo: G. Brocklehurst.