Lord Napier says, that when he was in the Mediterranean, some years ago, and during an awful thunderstorm, he was retiring to rest, when he heard suddenly a cry, from those aloft, of “St. Elmo and St. Anne!” which induced him again to go on deck. On observing the appearance of the masts, the maintop-gallant-mast-head was completely enveloped in a blaze of pale phosphoric light; the other mast-heads presented a similar appearance; the flame preserving its intensity for eight or ten minutes, and then gradually becoming fainter. Yet this appearance, which superstition declared to be miraculous, was only electrical; for, while the solar heat is converting into vapour the water and moisture of the earth, electricity is freely disengaged. “The clouds which this power forms are in different electrical conditions, though the electricity of the atmosphere, when serene, is invariably the same. Hence the descent of clouds towards the earth, their mutual approach, the force of atmospherical currents, and the ever-varying agencies of heat and cold convert the aërial envelope of the globe into a complete electrical apparatus; spontaneously exhibiting, in a variety of forms, the play of the conflict of its antagonist powers. At the close of a sultry day, and above level plains, the opposite electricities of the earth and the air effect their re-union in noiseless flashes of lightning, illuminating, as it were, in far-spread sheets, the whole circuit of the horizon, and the entire canopy of the clouds. At other times, the same elements light up the arctic constellations with their restless wildfires--now diffusing their phosphoric flame, and flitting around in fitful gleams, and now shooting up their auroral columns, advancing, retreating, and contending, as if in mimicry of mortal strife.”[I] That electricity and magnetism are identical, is evident from many experiments. If a sewing-needle be placed in a wire, twisted in that form called a helix, and a shock of electricity be then passed through it, from a Leyden jar, the needle will be magnetized. The form of the wire, and the manner of placing the needle, are shown in the figure. [Illustration] [Illustration] Again, if M be a piece of soft iron, of a horse-shoe shape, and surrounded with copper-wire covered with a non-conducting substance, it will become powerfully magnetic on connecting the ends of the wire with a galvanic battery. If this be only of a moderate size, and a keeper, I, be attached to M, it will suspend W, representing a very heavy weight.