SUMMER STORMS.
AMONG the remarkable features of the thunderstorms which broke over London on Friday and over various parts of the country on Saturday last week the most extra- ordinary were the tempests of dust and wind which swept in front of them. These tempests, doubtless naturally enough, appear to have preceded the storms of both days, but, for whatever reason, the rain in most places after Saturday's storms seems to have been not nearly so heavy as on Friday. On Friday in London the rain fell in torrents, and the weather records of the afternoon taken in South Kensington are astonishing. About five o'clock there was a wind blowing at less than ten miles an hour. The barometer just before five gave a sudden jump of six hundredths of an inch, and im- mediately the wind began to rise, until by quarter past five the squalls bad reached a velocity of 54 miles an hour. Ina quarter of an hour, therefore, the wind had changed from a light breeze to within two miles of the rate which, according to the Beaufort scale, constitutes a "storm." In the Beaufort scale, of course, the force of a wind is measured in the numbers 0 to 12, and not in miles ; but the Meteorological Office reckons a wind of 8-9, which Admiral Beaufort counted a gale, as travelling between 38 and 55 miles an hour. A wind of 56 to 75 miles is counted a storm, and above 75 miles per hour a hurricane. But the wind was not the only remarkable feature of Fridays weather. After the squalls came the rain, of which 1.1 inches fell in a quarter of an hour ; that is, at the rate of nearly 41 inches per hour. Then the thermometer in the quarter of an hour from 5.25 to 5.40 dropped 22 degrees, and so ended one of the most remarkable " samples " of weather recorded even in our surprising climate.
Saturday's storms broke over different centres, but in nearly all there was the same tremendous wind. It may, perhaps, be interesting to describe the storm, as the writer experienced it, in a rather exposed position on the side of a hill some 400 feet or more above sea-level. The day had been intensely hot and sultry, and about seven o'clock, when the wind had dropped to a dead calm, the sound of distant thunder began to grow nearer. Great masses of steel-blue clouds came rolling up from the south, seamed and slashed with white, with ominous gaps and ledges of vapour turning and reeling as the clouds drove up over the whole sky above. Still the thunder was nothing more than a rumble, and the interval between the scarcely seen flashes of lightning and the peal that followed was so long that the storm, wherever it was going on, was evidently a great distance away. Between the rolls of thunder the silence was intense; not a bird chirped, not a leaf stirred. And then, without a moment's warning, there leapt up from the earth a quarter of a mile away a great red pillar of dust which swept with a roar up the hill; dust uprose before it as it came, and in a second all round the house it was blow- ing a gale. The larches in the garden and the wood behind bent like blades of wheat ; doors in the house blew to like guns ; the remains of a bonfire near the stables which had been lighted to burn the green of felled larches burst into a cone of flame. In the storm of sand which was driving in the first thing to do was to close all the doors and windows of the house, and three people rushing along the passages found that it was only possible to shut the windows by pushing hard against the wind, otherwise they would have crashed and broken. The writer, trying to close a garden door which opens into the house, could only manage it by throwing his whole weight on the handle; then it seemed as if the lock must break when it was closed. Outside the gardener, blind with sand, tried to cover the bonfire with earth ; the earth was blown out of his shovel. It was the hardest fight to make any headway at all out of doors ; a child surely would have been blown over. So the storm drove on for, perhaps, five or six minutes, with the whole air red with sand ; then the squall dropped and the larches straightened, and there fol- lowed a mere breeze; then came a light shower of rain and a clear sky. And all through there had been no lightning and no thunder, beyond the fitful flashes over the downs, miles away ; merely the house had stood through what seemed like a hurricane, and every window-ledge and wainscoting was coated and drifted with sand.
It was the most interesting storm of the writer's experience ; but when is a thunderstorm not interesting P There is always in those tense moments before the storm actually breaks, with the ugly gaps rolling in the blackened sky and all the creatures silent in the fields and trees, a sense somewhere of the world coming to an end, of all kinds of possibilities belonging to a central mystery about which nothing can be calculated. And, of course, thunderstorms do, as a fact, remain without a full explanation which will assign all the observed effects to their proper causes. We know something about thunder and lightning, but it does not amount to very much, and "theories of thunderstorms" are still put forward to be compared with and be displaced by other theories. Some of these theories have been collected into a chapter in a well-arranged and comprehensive book on " Weather Science " by Mr. F. W. Henkel (Fisher Unwin, 6s. net), and one of the most recent happens also to be one which is fairly easy for the layman ignorant of electricity to understand. Its author is Dr. Simpson, of the Indian Meteoro- logical Department, and Mr. Henkel shortly explains it. "He supposes that upward currents of air prevent rain that would otherwise be deposited from falling. The rain-drops grow through cycles of growth,' then break up with separation of electricity, until their charge is so great as to produce a gradient of more than 30,000 volts per centimetre. Then the lightning flashes and the accumulation is neutralized over a limited area; the process goes on again, another flash takes place, and so on, till equilibrium is finally established and the storm ceases." Another interesting theory is that of Dr. S. P. Thompson. This begins with the fact that the clouds are usually more or less charged with electricity, which is mainly derived from evaporation going on at the earth's surface. The minute particles of water vapour floating in the air become more highly charged, and as they fall they coalesce. This means that the larger drops proportionately more highly charged find their way to the lower strata of a cloud, so that the electrification of the lower surfaces of the cloud becomes greater and greater, while the earth below " becomes charged oppositely by influence ; the layer of air between act- ing as the dielectric, the whole arrangement will become, as it were, a kind of condenser. After a time the difference of potential will be so great that the air between will give way, and a disruptive charge take place along the path of least resistance." And the path of least resistance may very well be through a dozen different substances other than air. The electric current will find its way along metal more easily than through a mixture of gases, just as water would filter through a crack in masonry filled with sand. We turn with interest to learn what Mr. Henkel can tell us of the latest theories of lightning conductors, to find that science is still in search of the perfect conductor and of the perfect system for arranging conductors. Iron, on the whole, is to be preferred to copper (and it is also cheaper); but even so, there are difficulties with iron. Lightning will not always jump on or down your iron conductors or any kind of conductor at all ; there are certain kinds of flashes which nobody seems able to do anything with—they just go where they please. And there seems to be a tendency among experts to approve, instead of the copper bands leading down from chimneys to earth plates in the soil, a sort of network or skeleton of rods or wires enclosing the building which it is desired to protect. But this is evidently a most complicated business. All the metal in the house has to be connected up with the network, so that you case your house in a kind of birdcage and then prick the wires of the cage through the walls to touch your pipes and fireplaces, and presumably your bedsteads. Thus encased you are said to be safer than with the plain copper bands. But it is not an inspiriting prospect for the householder, and he may possibly decide with his architect that it may be as well, after all, to have no lightning conductors and to chance it. Even with the best kind of bird- cage conductor he will always have to run the risk of that particular kind of flash about which nothing is known except that it will not obey the rules as we know them.
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