l 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