Science Siftings

New Zealand Tablet, Volume LII, Issue 35, 16 September 1925, Page 62

Science Siftings

L (Bi Volt)

, Harnessed Lightning. Few people have "a clear idea of the principles governing the use of lightning conductors. : An ordinary piece of wire used as a conductor would be less useful in a severe thunderstorm than a single water-pipe on » house would be in coping with a waterspout. Nearly all lightning strokes are characterised by numerous side flashes, and these have to be provided for. All the metal work on a building is interconnected.. The lightning conductor on the chimney or turret is joined perhaps to the rain-water pipes, these in turn being linked up with the iron railings round the building, and so on. In this way the flashes thrown off by lightning strokes are collected and guided safely to earth. Many people imagine that the end of a conductor is simply buried a few feet in the ground and left to take care of itself. If this were done, the soil would soon be burned up, leaving the conductor almost useless. In ground that is permanently moist, large copper plates are buried and the connections made to these. In dry soil a tube filled with charcoal is used. How Thunderstorms Start. "When the sun shines warmly upon sea or land it draws up moisture in the form of tiny globules too small for the eye to see. The warmer the air the greater the number of these globules it is able to hold in suspension. It is, of course, this moisture that causes rain. But before a raindrop can form it must have a nucleus, or centre. This is provided by the tiny specks of dust that float in the atmosphere. So tiny are these specks that each is no more than one forty-thousandth of an inch in diameter, and a cubic foot of saturated air may contain a thousand millions of them. Moisture rising in warm air reaches colder layers, and becomes visible as clouds. A cloud may be likened to a damp sponge' that must be squeezed before water comes out of it. The squeezing is done by cold, either a cold hilltop or a current of cold air. So raindrops are formed and at once begin to fall. > But in falling they may meet fresh updraughts of air, and so be pushed or drawn upwards again. If pushed up to a great height the drops may be frozen into lumps of ice and finally fall in the shape of hail. Water is a liquid of only moderate density, so the size of each drop is limited. No drop can be more . than one-fifth of an inch in diameter. If it grows bigger it splits. In splitting it releases negative electricity, and itself gains a positive charge. But electricity, like water, finds its own level. This process is always going on, every leaf and grass, blade acting as silent conductors. It is only when the tension becomes too great—when a cloud is overwhelmingly charged—that lightning flashes and we have .what we call a thunderstorm. What an Anticyclone Is. v Now that summer is approaching and outdoor pursuits are in season again, the wea-

ther forecasts given in the newspapers and ; announced on the wireless are receiving more attention than usual. The technical terai: : \ : ~ that occur in such reports are puling® jS many peoples - ' ? A glance at a weather map will show it "to be traversed by several heavy lines known as isobars. The word i s from the Greek, and \. the lines serve to join up places where the barometer is registering the same pressure at the time of preparing the map. \ ; Again, the general idea of a cyclone i s that it is a* severe hurricane, dangerous to life - and property. Actually, a cyclone is an area of low pressure shaped somewhat like a cone, so that the lowest pressure is 'in the centre. - The winds, which are not necessarily strong, blow spirally round this centre, creating an atmospheric condition similar to a whirlpool seen in water. * Cyclone and depression are identical terms, so that the oft-heard wireless announcement that "a depression is spreading from -the ■ Atlantic" may be taken as a hint to wear a mackintosh. Conversely, when an anticyclone is on the way, one need not take this precaution. An anticyclone, as its name suggests, is the opposite to a cyclone; that is, it is an area of high pressure, also cone-shaped, with the highest pressure in the centre. The winds levolve xound this area, so that it may be compared to an invertel whirlpool. In the area of an anticyclone the air descends and becomes dry in the. process. Radiation of warmth and cold takes place easily. In winter such a phenomenon produces clear air with periods of frost that cause fogs in towns and in damp places. In, summer the approach of an anticyclone can be taken to indicate fine weather. x7^~ .. Tit Bits (London*).'