Page:Handbook of Meteorology.djvu/122



Just as water, by seeking its own level, acquires an even and uniform pressure, so the electricity of the air seeks an even and uniform potential. If a body of cold, dry and highly charged air flows into a region of low potential, or into one oppositely charged, an interchange, or flow of electricity, results. The interchange may be so quiet that it escapes notice; on the other hand, it may be violent enough to produce strong electrical discharges.

The origin and source of atmospheric electricity is still a problem to be solved; so also is the origin of earth electricity. To the best of human knowledge, the earth is constantly giving off negative electricity, and receiving none in return, except that which is brought down by rain, or by snow, or by lightning strokes which pass from the clouds to the earth. The reason therefor is not known.

It has been found that a rainstorm carries to the earth about 3.5 times as much positive as negative electricity; and that positively charged snow falls more frequently than that which is negatively charged. A reason therefor certainly exists, but it is not known. The breaking of large drops of water into spray is accompanied by the production both of positive and negative electricity. Conversely, when fine spray is charged with electricity, the spray immediately coalesces into very large drops of water.

Extra-terrestrial Influences in Atmospheric Electricity.—The fact that rapid movements in sun spots and similar