7. Thus a circulation of air is kept up in our atmosphere, as in the room above-mentioned.
8. That heavier and lighter air may move in currents of different and even opposite direction, appears sometimes by the clouds that happen to be in those currents, as plainly as by the smoke in the experiment above-mentioned. Also in opening a door between two chambers, one of which has been warmed, by holding a candle near the top, near the bottom, and near the middle, you will find a strong current of warm air passing out of the warmed room above, and another of cool air entering below; while in the middle there is little or no motion.
9. The great quantity of vapour rising between the tropics forms clouds, which contain much electricity.
Some of them fall in rain, before they come to the polar regions.
10. If the rain be received in an isolated vessel, the vessel will be electrified; for every drop brings down some electricity with it.
11. The same is done by snow or hail.
12. The electricity so descending, in temperate climates, is received and imbibed by the earth.
13. If the clouds are not sufficiently discharged by this gradual operation, they sometimes discharge themselves suddenly by striking into the earth, where the earth is fit to receive their electricity.
14. The earth in temperate and warm climates is generally fit to receive it, being a good conductor.