Alexander George McAdie
(4 Aug 1863 - 1 Nov 1943)
THE STORAGE BATTERY OF THE AIR.
by Alexander McAdie, M.A.
from Harpers New Monthly Magazine (Jul 1894)
[p.216] To ask if we can use lightning, at this the close of the nineteenth century, may seem like a trite question. For do we not all know that the most unique of the many philosophers of the eighteenth century certainly did make use of lightning with more or less success? Aside from the kite experiment, Franklin made other experiments with lightning, some of them looking especially to a practical application of the apparently lawless energy of the heavens. For instance, in September, 1752, he erected upon his house in Philadelphia an iron rod with two bells, “to give notice when the rod should be electrified.” A little later, with this same apparatus and a Leyden jar, he undeniably demonstrated, from a popular standpoint, the practicability of “bottling up” the electricity of the air.
The lamentable killing of the young Russian, Richmann, on August 6, 1755, while experimenting along the lines indicated and followed by Franklin, put a stop for a while to direct experimentation with lightning. With a friend standing not quite two feet away, Richmann was watching the indications of his electrometer when the flash occurred which killed him. The friend was stunned, but not otherwise injured. This accident, had it occurred at the end of the nineteenth century—an era of electrothanasia—would certainly have led to applications for patents improving the expensive, cumbersome apparatus now in use as a deterrent to crime.
Of those to whom patents have been granted in connection with lightning, almost all have had in mind only the conduction of the flash to the ground, and its expeditious burial there, with a minimum of danger to life and property. Patents have been granted for “diffusers,” whereby the lightning is to be distributed over a larger area than, presumably, it could find unassisted. Other patents, particularly in connection with points, cover what maybe called “neutralizing effects”; but until quite lately there was an entire absence of any attempt to use lightning practically.
With the introduction of electric lighting came, under the name “arresters,” devices for making lightning work; for example, automatically closing and opening auxiliary circuits. So prettily is lightning harnessed in these circuits that not only is the line relieved of charge for the time being without damage, but any dynamo short circuit resulting is promptly interrupted, and all made ready for the next flash. But with lightning-rods we have none of this.
Two or three years ago an application was made for a patent in which the inventor proposed, in simple English, to place material in the path of the flash, and thus use up its energy. We refer to it only because it marks a radical change [p.217] in the methods of protection, and is probably the pioneer of a long series.
Dr. Lodge’s lectures before the Society of Arts, remarkable for the spirit with which he assailed the work of the Lightning-rod Conference, and his clean-cut laboratory work at Liverpool—he is professor of physics in University College there—taught us to look squarely at the character of the flash. One interesting historical coincidence which occurred in the summer of 1888, when the problem of the flash had resolved itself into the study of electrical waves along wires, must not pass unnoticed. In a postscript written from Cortina in the Tyrol he tells how this long-neglected question of the nature of lightning had led to the same end as the work of Hertz—the finest piece of experimental work of our time—namely, the identification and measurement of ether waves. With characteristic frankness, at the September meeting of the British Association, Lodge hastened to acknowledge the superiority of Hertz’s method of demonstration to his own. But to us the interesting fact remains that the study of lightning had shown the truth of Clerk Maxwell’s theory of light.
Let us now follow Lodge in his estimate of the total maximum energy of a given area of cloud-air-earth condenser. The air will stand a strain of about 9600 grains per square foot before breaking. That is, the flash will occur when the electrical pull amounts to this 1.37 pounds per square foot. For the energy of a cubic mile of strained air just before the flash we have, then, about seventy million foot-tons. The average thunder-head or cumulo-nimbus cloud is not a mile high, however. For a small cloud, one a hundred yards square, and distant only a quarter of a mile, we would get about three hundred horse-power. Now a flash even a quarter of a mile long means a potential of many million volts. We cannot at present measure this directly, but we can determine the potential of the air within certain limits on any day, thunder-storm or no thunder-storm.
In 1885, at Blue Hill Observatory, and in subsequent years, we measured the potential of the air with insulated water-dropping collectors, after the methods of Thomson (now Kelvin) and Mascart. The top of the hill is six hundred feet above the surrounding country; but with Franklin’s idea of reaching out a little farther from earth, I ventured to use at times a large kite, tin-foiled, and for kite string some five hundred feet of hemp fish-line wrapped about with fine uncovered copper wire. During thunder-storms the sparking and sizzling at the electrometer end of the kite string were incessant and startling. And even on cloudless days I found it possible to draw sparks, reading at the same time on the electrometer from minute to minute the electrification of the air in volts. In 1886 and 1887, in some investigations carried on by the Chief Signal Officer, and more immediately under the supervision of Professor Mendenhall, I experimented at the top of the Washington Monument, at that time the highest edifice in the world. The investigation continued many months, but perhaps days on which severe thunder-storms occurred were most impressive.
May 6, 1887.—Five hundred feet above the city streets. It is a warm afternoon, and looking from the west windows of the monument one sees through the near haze around Arlington and the Virginia hills, far to the southwest, say over Fairfax, a patch of dark cloud. It needs little experience to presage a thunder-squall. It is about twenty miles away, and may reach us in forty minutes, perhaps in less time. At ten minutes to three o’clock (see diagram) the clouds are overhead, and this is the last we shall see of the world outside until the storm is over, for it is necessary that the heavy marble doors be swung to. And now there is no light in the monument save the reflected beam travelling along the ground-glass scale, indicating the movement of the electrometer needle. One small opening on the south face of the monument is provided, through which projects the nozzle of the collector. We can hear the wind rising. The needle steadily mounts up to the thousand-volt degree, showing that the electrical tension of the air is increasing. Suddenly the needle flies to the other side of the scale, meaning that, like a piece of over-strained rubber, the air has snapped. The pull becomes negative, i.e., in an opposite direction. Now the needle dances, and we hear the rumble of distant thunder.
It will not be out of place to allude to the sense of awe which steals over one working all alone at the top of this high edifice during a thunder-squall. The wind tears fiercely around the south and [p.218] west sides of the pyramidion. The cap of the monument has twice been struck, and on one occasion the top stone was fractured. The heavy marble shutters, which you have slowly and laboriously swung into place and securely fastened with bolts, are beaten against so furiously that you are doubtful of their remaining in place. With every flash of lightning (although we are in the dark we can time the lightning) there is a sharper “click” than usual, and we catch the fleeting reflection of a spark in the electrometer. On one occasion, rigging up a wire from the iron floor and elevator shaft to within an eighth of an inch of the collector, I counted over a hundred sparks per minute. If we place the eye close, but not too close, to the little peep-hole through which the nozzle of the collector protrudes, we can see the fine stream of water twisting and breaking into spray, and each time it lightens becoming normal, quick as the flash itself, but only to rapidly twist and distort again.
The diagram shows the fluctuations of the potential during such a storm. The deflections at times are beyond the scale limits. Values of three thousand and four thousand volts are given here, but within the past year at the Eiffel Tower values of over ten thousand volts have been noted. It is not absolutely necessary to go to the top of a tower to come in contact with the potential. With suitable apparatus, good records can be obtained from a second or third story window. In general the potential increases as we ascend. Some idea of the rate of increase can be gained from the following comparison.
Time, a day in November. The two stations about 500 feet and 45 feet respectively.
|1.30 P.M.||900 volts.||216 volts.||684 volts.|
|1.32 "||888 "||246 "||642 "|
|1.34 "||900 "||216 "||684 "|
|1.36 "||862 "||246 "||616 "|
|1.38 "||875 "||240 "||635 "|
|1.40 "||825 "||222 "||603 "|
It being beyond dispute, then, that high potentials can be obtained from the air, the question naturally ensuing is, Can we not use them? With three or four sparks as small as those mentioned above a large fruit jar can be cleared of smoke with which it has previously been filled. Perhaps nature repeats this on a large scale with lightning, and clarifies a foul dust-laden atmosphere with these great sparks. It may be, too, that these flashes are all needed, and to attempt to divert them would be unwise. Be that as it may, we are living in an age of “step-up” and “step-down” transformers; an age when, for the first time in centuries, we are perilously near duplicating lightning. Until [p.219] recently we studied lightning only in miniature. Professor Elihu Thomson was kind enough to show me in his Lynn laboratory, two summers ago, some of his larger home-made lightning. Indeed potentials of 100,000 volts are less rare today than potentials of 5000 volts were five years ago. All who saw the Thomson and Tesla exhibits at the Electrical Building, Chicago, will easily believe that it is within our power to turn the fleeting high-potential lightning into a current of lower potential and use it.
Professor Trowbridge of Harvard University, in a discussion of some photographic negatives, shows that “the discharge follows exactly the same path in air for three hundred-thousandths of a second,” and adds that “it is probable that an ordinary discharge of lightning of a few hundred feet in length could light for an instant many thousand incandescent lamps if it were properly transformed by means of a step-down transformer.”
We said above that we timed the flashes without seeing them. It is easily done. Two observers compare watches; one goes into the open and times each flash; the other, in the dark room, times the more violent movements of the needle. The relation is obvious, although there are more fluctuations than flashes. This I explain by assuming that there are discharges unseen, but not unfelt. The eye alone cannot give a complete history of the myriad minor flashes during a thunderstorm. The charred though to us intensely brilliant crack in the air which we call lightning is but a great splash in the ether ocean. The waves and ripples come tumbling along in all directions, spreading rapidly, ay, very rapidly, nearly two hundred thousand miles per second. Given a proper resonator, and the waves will do work. If my reader keep every sense on the alert, he may happen on some strange illustration of work done by lightning, now all unsuspected. In the tinkling of the telephone bell, the blinking of an incandescent lamp, the melting of a fuse, or the tiny spark from a gas-pipe or loose wire, is the constant proof that there are more things going on between heaven and earth during a thunder-storm than most of us dream of in our philosophy.
- 4 Aug - short biography, births, deaths and events on date of McAdie's birth.
- Articles written by Alexander McAdie
- Theory and Practise of Frost Fighting - article by Alexander McAdie from Scientific Monthly (1915)
- Needless Alarm During Thunderstorms - article by Alexander McAdie from Century Magazine (1899).
- What is an Aurora - article by Alexander McAdie from The Century Magazine (1897).
- Muir of the Mountains - Alexander McAdie writing about John Muir in Sierra Club Bulletin (Jan 1916).
- Franklin's Kite Experiment With Modern Apparatus - article by Alexander McAdie from Popular Science (1897).
- Making the Weather, by Alexander G. McAdie. - book suggestion.