IX. ARTIFICIAL WARMTH.--RING AND STAPLE.--THE FAN 412 X. WATER, AND MEANS OF PROCURING IT 422 XI. AËROSTATICS.--WEIGHT OF AIR.--EXPANSION BY HEAT 436 XII. DITTO CONTINUED 447 XIII. TELESCOPIC TUBES.--DIRECT ACTION.--DISTRIBUTION OF WEIGHT.--TREE-CLIMBING.--THE WHEEL 460 XIV. PAPER AND MOULDING 472 XV. ELECTRICITY AND GALVANISM 482 XVI. TILLAGE.--DRAINAGE.--SPIRAL PRINCIPLE.--CENTRIFUGAL FORCE 492 XVII. OSCILLATION.--UNITED STRENGTH.--THE DOME 504 ACOUSTICS. I. PERCUSSION.--THE STRING AND REED.--THE TRUMPET.--EAR-TRUMPET.--STETHOSCOPE 513 NAUTICAL. CHAPTER I. Poetry and Science.--The Paper Nautilus and the Sail.--Montgomery’s “Pelican Island.”--The Nautilus replaced by the Velella.--The Sailing Raft of Nature and Art.--Description of a Velella Fleet off Tenby.--The Natural Raft and its Sail.--The Boats of Nature and Art.--Man’s first Idea of a Boat.--The Kruman’s Canoe and the _Great Eastern_.--Gradual Development of the Boat.--The Outrigger Canoe a Mixture of Raft and Boat.--Natural Boats.--The Water-snails.--The Sea-anemones.--The Egg-boat of the Gnat.--The Skin-boat of the same Insect.--Shape and Properties of the Life-boat anticipated in Nature.--Natural Boat of the Stratiomys. THE RAFT. It has been frequently said that the modern developments of science are gradually destroying many of the poetical elements of our daily lives, and in consequence are reducing us to a dead level of prosaic commonplace, in which existence is scarcely worth having. The first part of this rather sweeping assertion is perfectly true, but, as we shall presently see, the second portion is absolutely untrue. Science has certainly destroyed, and is destroying, many of the poetic fancies which made a part of daily life. It must have been a considerable shock to the mind of an ancient philosopher when he found himself deprived of the semi-spiritual, semi-human beings with which the earth and water were thought to be peopled. And even in our own time and country there is in many places a still lingering belief in the existence of good and bad fairies inhabiting lake, wood, and glen, the successors of the Naiads and Dryads, the Fauns and Satyrs, of the former time. Many persons will doubtless be surprised, even in these days, to hear that the dreaded Maelström is quite as fabulous as the Symplegades or Scylla and Charybdis, and that the well-known tale of Edgar Poe is absolutely without foundation. Perhaps one of the prettiest legends in natural history is that of the Paper Nautilus, with which so much poetry is associated. We have all been accustomed from childhood to Pope’s well-known lines beginning--