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] |
| A Ship attacked by a Sword-fish | [256] |
| The Safety-lamp | [259] |
| The Dust we have to Breathe | [265] |
| Photographic Ghosts | [267] |
| The Oxford and Cambridge Rowing Styles | [269] |
| Betting on Horse Races: or, the State of the Odds | [274] |
| Squaring the Circle | [288] |
| A New Theory of Achilles’ Shield | [297] |
LIGHT SCIENCE FOR LEISURE HOURS.
STRANGE DISCOVERIES RESPECTING THE AURORA.
The brilliant streamers of coloured light which wave at certain seasons over the heavens have long since been recognised as among the most singular and impressive of all the phenomena which the skies present to our view. There is something surpassingly beautiful in the appearance of the true ‘auroral curtain.’ Fringed with coloured streamers, it waves to and fro as though shaken by some unseen hand. Then from end to end there pass a succession of undulations, the folds of the curtain interwrapping and forming a series of graceful curves. Suddenly, and as by magic, there succeeds a perfect stillness, as though the unseen power which had been displaying the varied beauties of the auroral curtain were resting for a moment. But even while the motion of the curtain is stilled we see its light mysteriously waxing and waning. Then, as we gaze, fresh waves of disturbance traverse the magic canopy. Startling coruscations add splendour to the scene, while the noble span of the auroral arch, from which the waving curtain seems to depend, gives a grandeur to the spectacle which no words can adequately describe. Gradually, however, the celestial fires which have illuminated the gorgeous arch seem to die out. The luminous zone breaks up. The scene of the display becomes covered with scattered streaks and patches of ashen grey light, which hang like clouds over the northern heavens. Then these in turn disappear, and nothing remains of the brilliant spectacle but a dark smoke-like segment on the horizon.
Such is the aurora as seen in arctic or antarctic regions, where the phenomenon appears in its fullest beauty. Even in our own latitudes, however, strikingly beautiful auroral displays may sometimes be witnessed. Yet those who have seen the spectacle presented near the true home of the aurora, recognise in other auroras a want of the fulness and splendour of colour which form the most striking features of the arctic and antarctic auroral curtains.
Physicists long since recognised in the aurora a phenomenon of more than local, of more even than terrestrial, significance. They learned to associate it with relations which affect the whole planetary scheme. Let us inquire how this had come about.
So long as men merely studied the appearances presented by the aurora, so long, in fact, as they merely regarded the phenomenon as a local display, they could form no adequate conception of its importance. The circumstance which first revealed something of the true character of the aurora was one which seemed to promise little.