Page:Popular Science Monthly Volume 43.djvu/476

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THE POPULAR SCIENCE MONTHLY.

"Think now," says Lodge, "of a cloud and of the earth under it as forming the two coats of a Leyden jar, in the dielectric of which houses and people exist; we now have to consider what determines a discharge, and what happens when a discharge occurs. The maximum tension which air can stand is one half gramme weight per square centimetre. At whatever point the electric tension rises to this value, smash goes the air. The breakage need not amount to a flash, it must give way along a great length to cause a Hash; if the break is only local, nothing more than a brush or fizz need be seen. But when a flash does occur it must be the weakest spot which gives way first—the place of maximum tension—and this is commonly on the smallest knob or surface which rears itself into the space between the dielectrics. If there be a number of small knobs or points, the glows and brushes become so numerous that the tension is greatly relieved and the whole of a moderate thunder-cloud might be discharged in this way without the least violence.... But sometimes a flash will descend so quickly or it will have such a tremendous store of energy to get rid of that no points are sufficiently rapid for the work, and crash it all comes at once. One specially noteworthy case is when one cloud sparks into another and thence to the ground; or in general whenever electric strain is thrown quite suddenly upon a layer of air."

PSM V43 D476 Curve showing the electrical potential of the atmosphere.jpg
Curve Showing Electrical Potential of the Atmosphere.

Thus, then, we begin to see that much will depend upon the character of the flash. There are many flashes, I believe, that the body could experience without very serious consequences; and there are many that will rive solid granite and shatter in splinters the heaviest masonry. The impulsive rush discharge shown on the preceding page was doubtless a flash of the latter character; and on the other hand, with a kite in air during thunderstorms with a wire connection to the ground I have experienced sharp shocks with lightning