In preparing these Essays, my chief object has been to present scientific truths in a light and readable form—clearly and simply, but with an exact adherence to the facts as I see them. I have followed—here and always—the rule of trying to explain my meaning precisely as I should wish others to explain, to myself, matters with which I was unfamiliar. Hence I have avoided that excessive simplicity which some seem to consider absolutely essential in scientific essays intended for general perusal, but which is often even more perplexing than a too technical style. The chief rule I have followed, in order to make my descriptions clear, has been to endeavour to make each sentence bear one meaning, and one only. Speaking as a reader, and especially as a reader of scientific books, I venture to express an earnest wish that this simple rule were never infringed, even to meet the requirements of style. It will hardly be necessary to mention that several of the shorter Essays are rather intended to amuse than to instruct. The Essay on the influence which marriage has been supposed to exert on the death-rate is the one referred to by Mr. Darwin at page 176 (vol. i.) of his ‘Descent of Man.’ RICHARD A. PROCTOR. LONDON: _May_ 1871. CONTENTS. PAGE STRANGE DISCOVERIES RESPECTING THE AURORA 1 THE EARTH A MAGNET 14 OUR CHIEF TIME-PIECE LOSING TIME 30 ENCKE THE ASTRONOMER 46 VENUS ON THE SUN’S FACE 49 BRITAIN’S COAL CELLARS 72 THE SECRET OF THE NORTH POLE 97 IS THE GULF STREAM A MYTH? 114 FLOODS IN SWITZERLAND 133 A GREAT TIDAL WAVE 138 DEEP-SEA DREDGINGS 142 THE TUNNEL THROUGH MONT CENIS 148 TORNADOES 153 VESUVIUS 167 THE EARTHQUAKE IN PERU 189 THE GREATEST SEA-WAVE EVER KNOWN 194 THE USEFULNESS OF EARTHQUAKES 211 THE FORCING POWER OF RAIN 225 A SHOWER OF SNOW-CRYSTALS 230 LONG SHOTS 233 INFLUENCE OF MARRIAGE ON THE DEATH-RATE 238 THE TOPOGRAPHICAL SURVEY OF INDIA 244