Since air is a non-conductor, it does not convey the electricity from the clouds to the earth, but it acquires from them an opposite kind, and when the tension is very great the force of the electricity becomes irresistible, and an interchange takes place between the clouds and the earth; but so rapid is the motion of lightning, that it is difficult to ascertain whether it goes from the clouds to the earth or shoots upwards from the earth to the clouds, though there can be no doubt that it does both. In a storm that occurred at Manchester in June 1835, the lightning was observed to issue from various points of a road, attended by explosions as if pistols had been fired out of the ground, and a man seems to have been killed by one of these explosions taking place under his foot. M. Gay Lussac ascertained that a flash of lightning sometimes darts more than three miles in a straight line. A person may be killed by lightning, although the explosion takes place at a distance of twenty miles, by what is called the back stroke. Suppose that the two extremities of a highly charged cloud hang down towards the earth, they will repel the electricity from the earth’s surface if it be of the same kind with their own, and will attract the other kind; and if a discharge should suddenly take place at one end of the cloud, the equilibrium will be instantly restored by a flash at that point of the earth which is under the other. Though the back stroke is often sufficiently powerful to destroy life, it is never so terrible in its effects as the direct stroke, which is often of inconceivable intensity. Instances have occurred when large masses of iron and stone, and even many feet of a stone wall, have been carried to a considerable distance by a stroke of lightning. Rocks and the tops of mountains often bear the marks of fusion from its intense heat; and occasionally vitreous tubes descending many feet into banks of sand mark its path. Dr. Fiedler exhibited several of these fulgorites in London of considerable length, which had been dug out of the sandy plains of Silesia and Eastern Prussia. One found at Paderborn was forty feet long. Their ramifications generally terminate in pools or springs of water below the sand, which are supposed to determine the course of the lightning. No doubt the soil and substrata must influence its direction, since it is found by experience that places which have been once struck by lightning are often struck again. An insulated conductor on the approach of a storm gives out such quantities of sparks that it is dangerous to approach it, as was fatally experienced by Professor Richman at Petersburg, who was struck dead by a globe of fire from the extremity of a conductor, while making experiments on atmospheric electricity. Copper conductors afford the best protection, especially if they expose a broad surface, since electricity is conveyed along the surface of bodies. There is no instance of an electric cloud of high tension being dispelled by a conductor, yet those invented by Sir William Snow Harris, and universally employed in the navy, afford a complete protection in the most imminent danger. The Shannon, a 50-gun frigate, commanded by the brave and lamented Sir William Peel, was enveloped in a thunder-storm when about 90 miles to the north-west of Java. It began at fifty minutes past four in the afternoon; the ship was driven before the storm, in a high sea, amid streams of vivid lightning, deafening thunder, hail, and rain. At five o’clock an immense ball of fire covered the maintopgallant mast, ran up the royal pole, and exploded in the air with a terrific concussion, covering all the surrounding space with sparks of electric light, which were driven rapidly to leeward by the wind. Fifteen minutes later an immense mass of lightning struck the mainmast, attended by a violent gust of wind; and another heavy discharge fell on it a quarter of an hour afterwards. From that time till six o’clock the ship was continually encompassed by sharp forked lightning, accompanied by incessant peals of thunder. Though actually enveloped in electricity, and struck three times, neither the hull nor the rigging sustained the slightest injury.