ses thunder and lightning and the other phenomena of the same nature.
So much for thunder and lightning.
Book III
1
LET us explain the remaining operations of this secretion in the same way as we have treated the rest. When this exhalation is secreted in small and scattered quantities and frequently, and is transitory,Eden Hazard Drakt, and its constitution rare,Dame Moncler Loire, it gives rise to thunder and lightning. But if it is secreted in a body and is denser,Menn Moncler Zin, that is,Duke Waxed Bunda, less rare, we get a hurricane. The fact that it issues in body explains its violence: it is due to the rapidity of the secretion. Now when this secretion issues in a great and continuous current the result corresponds to what we get when the opposite development takes place and rain and a quantity of water are produced. As far as the matter from which they are developed goes both sets of phenomena are the same. As soon as a stimulus to the development of either potentiality appears, that of which there is the greater quantity present in the cloud is at once secreted from it, and there results either rain, or, if the other exhalation prevails, a hurricane.
Sometimes the exhalation in the cloud, when it is being secreted,Kurtki Peuterey, collides with another under circumstances like those found when a wind is forced from an open into a narrow space in a gateway or a road. It often happens in such cases that the first part of the moving body is deflected because of the resistance due either to the narrowness or to a contrary current,Canada Goose Mystique Parka, and so the wind forms a circle and eddy. It is prevented from advancing in a straight line: at the same time it is pushed on from behind; so it is compelled to move sideways in the direction of least resistance. The same thing happens to the next part, and the next,Fotball Snapback Hatter, and so on, till the series becomes one, that is,Lazio Drakt, till a circle is formed: for if a figure is described by a single motion that figure must itself be one. This is how eddies are generated on the earth, and the case is the same in the clouds as far as the beginning of them goes. Only here (as in the case of the hurricane which shakes off the cloud without cessation and becomes a continuous wind) the cloud follows the exhalation unbroken, and the exhalation,Damskie Barbour Liddesdale Kurtka, failing to break away from the cloud because of its density,Russland Drakt Barn, first moves in a circle for the reason given and then descends, because clouds are always densest on the side where the heat escapes. This phenomenon is called a whirlwind when it is colourless; and it is a sort of undigested hurricane. There is never a whirlwind when the weather is northerly,Saudi Arabia Drakt, nor a hurricane when there is snow. The reason is that all these phenomena are ‘wind’, and wind is a dry and warm evaporation. Now frost and cold prevail over this principle and quench it at its birth: that they do prevail is clear or there could be no snow or northerly rain,Arctic Parka, since these occur when the cold does prevail.
So the whirlwind originates in the failure of an incipient hurricane to escape from its cloud: it is due to the resistance which generates the eddy, and it consists in the spiral
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