"THIS boiling Fermentation of the Sea causes the Vapours to rise, which by the Intenseness of the circumambient Cold are condensed into thick Clouds, and fall down in Storms of Wind and Rain, first upon the Sea, from whence they rose, and then the attractive Power of the Mountain-cold, by a secret Magnetism between Vapour and Cold, attracts the waterish Vapours, intermixt with nitrous Particles, to the high Tops of Mountains and Hills, where they hang hovering in thick Fogs and waterish Mists, until the atmospherical Heat rarefies the nitrous Part of the Fog (which is always uppermost, and appears white and translucent) into brisk Gales of Wind, and the Intenseness of atmospherical Cold having attracted the Vapours into the colder Regions of the Air, where being condensed into Clouds, the Wind breaks, dissipates, and drives them before it, till they fall down in Rain, and water the Surface of the Earth. And this seems to be the Reason why, in _Egypt_, and those level Countries where they have no Mountains, they have little Wind and less Rain." XVIII. CLOUDS. _In Summer or Harvest, when the Wind has been South two or three Days, and it grows very hot, and you see Clouds rise with great white Tops like Towers, as if one were upon the Top of another, and joined together with black on the nether Side_, there will be Thunder and Rain suddenly. WE may very easily account for this Observation, because in Fact the Signs here mentioned are no other than Nature's apparatus for a Storm of Thunder and Lightning, which will be perfectly understood by attending a little to the Causes of these Meteors. Lightning is a great flame, very bright, extending every way to a great distance, suddenly darting upwards, there ending, so that it is only momentaneous. The Matter which produces the Fire, is the Oil of Plants, attenuated by the heat of the Day, and raised on high. Then whatever has exhaled from the Earth that is sulphureous or Oily, which is dispersed up and down in the Atmosphere, and is not continuous, is set on Fire by Turns, and the Flame dilates itself as far as the Tract of that Exhalation reaches. Some other Substance pendant and floating in the Air meets with this also, with which it excites an effervescence, takes Fire and flashes along with it. Thunder is another bright Flame, rising on a sudden, moving with great Velocity through the Air, according to any Determination upwards from the Earth horizontally, obliquely, downwards in a right Line, or in several right Lines as it were in serpentine Tracts joined at various Angles, and commonly ending with a loud Noise or Rattling.