ELECTRIC STORM, a sudden and violent change in the normal magnetic currents of the earth, with oscillations of potential, interfering with the action of telegraph and telephone in struments, sometimes suspending their opera tion and even diverting the current so as to stop trolley cars; called also magnetic storm. Without any advance warning the magnetic nee dles will swing a long way out of normal posi tions, because of the disturbed earth currents. The electric potential of the earth is ordinarily stated as zero, and all electric currents are meas ured from that basis or standard, which repre sents the balance that electricity seeks. The earth is a huge dynamo, with magnetic currents continually flowing, and it will absorb any amount of electric current that the machines of man can collect without any apparent effect on this vast storehouse of nature. But the sun is also a natural dynamo, of vastly greater ac tivities and subject to electric stresses of a vio lence far transcending anything we have or can experience on this earth. One of the ap parent effects of the electric and chemical ac tivities of the sun is displayed in the sun-spats, which occur there with irregular frequency, ap pearing to come and go in undetermined cycles. The cause of these sun-spots is largely conjec tural, but the view is generally accepted that they represent openings or vortices in the outer gaseous envelope of the sun. However this may be, it is apparent that they are in some way connected with the electric storms or violent changes of magnetism that occur on the earth. These electric stresses occur at intervals that cannot be predicted, but are comparatively fre quent, and perhaps once or twice a year the violence of the magnetic changes is sufficiently abnormal to be characterized as a great storm, which for a short time paralyzes the action of more or less electric machinery, much as a great storm of wind and rain paralyzes the traffic of a large city.
For the past 25 years or longer many scien tists and a number of observatories have been more or less engaged in studying the phenomena of these storms and have striven to formulate a correct theory of their origin and progress. The difficulty is not that reasons cannot be found for such irregularities of the earth's po tential, but rather that there are so many plaus ible explanations which cannot all be true, that the investigators are puzzled which clues to follow. Early observations disclosed a periodic ity in the electrical storms, that clearly tended to follow the displays of sun-spot activity. If these spots were the direct cause it would be reasonable to expect the following electrical storm on the earth to come at a definite interval; but the fact is that an electric storm always lags behind the sun-spot activity, and lags all the way from a few hours to a few days. While the average lag is about 38.4 hours, the lag in great storms is only about 20 hours, indicating that the more violent the influence the swifter the travel.
Another sort of evident periodicity in elec trical storms is their recurrence at periods of about a month. Some observers have figured numerous intervals corresponding with the lunar month, while others have noted a close correspondence with the synodic months of 29 and a fraction days, this synodic month repre senting the dates on which the earth, sun and moon come almost or quite into a direct line.
This suggests that the storms are influenced by the sun and moon jointly, or that in some way the moon directs these extraordinary electric activities of the sun toward this planet.
Certain other well-established phenomena have been established with reference to these storms. Not only are they coincident with sun-spots to a marked degree, but also with dis plays of the aurora borealis or ((northern lights." Evidently the aurora is but a visual evidence of magnetic disturbance. Another pertinent fact discovered is that the magnetic storm is about twict• as apt to occur in the night time as in daylight, which is accounted for on the supposition that the rays strike the earth's atmosphere at a great height and are deflected by the earth's magnetic currents, being mainly manifest on the hemisphere opposite the sun. They are by no means confined to the dark hemisphere; in fact they frequently strike the earth and circle it several times before their force is spent. Prof. L. A. Bauer, of the Car negie Institute at Washington, discovered that in two great electrical storms (in 1902 and 1903) the magnetism circled the earth at a speed of about 7,000 miles a second, requiring 3Y2 to 4 seconds only to complete the cir cumference. It had previously been supposed that all magnetic needles felt the storm at the same instant. He not only demonstrated this travel, but showed that some storms traveled from west to east, others from east to west Other things we know about electric storms are that the smaller storms are comparatively local, being termed equatorial storms and polar storms according to the portion of the earth's surface affected. There are also types recog nized as positive and negative storms.
Within recent years a new theory has de veloped, which may be summed up with the idea that pencil-shaped emanations or shafts of Roentgen or cathode rays, or perhaps of nega tively charged particles, are shot out by the sun during periods of sun-spots, and that when the earth runs into one of these the effect here is an electric storm. This hypothesis assumes that the same electric activities that produce sun-spots also produce these pencil-shaped shafts of rays and not that the sun-spots are responsible for them. Professor Bauer points out that the fact that electric storms may travel in either direction around the earth is against this pencil-like shaft theory, as these should intercept the earth always in the same way. The professor has also noted that these storms seem to break at a height of about 75 miles in the earth's atmosphere and that as they come closer to the surface their effects are felt more severely. He contends that the energy of elec tric storms is supplied by the earth itself and not by the sun or sun-spots; that the same ac tivities in the sun that cause sun-spots, set in motion the electric storms very much as a trig ger sets in motion the activities of the powder in a gun.
• Prof. Kr. Birkeland, of Christiania, has made exhaustive experiments with vacuum tube apparatus of his own designing, in the effort to prove the theory of cathode ray origin or something similar. He has succeeded in dupli cating much of the phenomena of the electric storm and made many valuable records, but his theories have not been generally accepted.