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magnetism produced is so distributed as to give a perfectly symmetrical torque on the motor, just as though it were run from a polyphase circuit; a point which I think justifies me in the remark I made at the beginning,-that the monocyclic system is to be regarded, not altogether as a modified and glorified single-phase; nor, again, as a decrepit and disreputable polyphase system, but rather as in a class by itself. On motion, the meeting adjourned.
Mr. Seely moved that a vote of thanks be extended to the ladies of Cleveland for the reception they had extended to the ladies accompanying the gentlemen in attendance at the meeting.
SPECIAL EVENING SESSION,
LECTURE BY ALEXANDER JAY WURTS ON LIGHTNING ARRESTERS AND WHY
THEY SOMETIMES FAIL.
When the first telegraph lines were installed it was noticed that the instruments frequently became damaged during thunder storms. The wires were charged with static electricity, which, in preference to following many turns of wire through the instruments to earth, would puncture the insulation between consecutive convolutions, and thus shortcircuit the coils. Besides this damage to the instruments, it was noticed that the static charge would sometimes spring from the line or other metallic parts of the circuit to neighboring conducting objects, such as nails, iron pipes and the like. It was also noticed that when discharge occurred in this manner, the instruments were not damaged. In other words, these neighboring objects formed the by-paths for the discharge, and, in a measure, offered protection to the instruments. As a consequence of such observation, artificial by-paths were constructed, which consisted of two metal electrodes separated by a small air-space, one of which was connected to the line, the other to earth, and thus the first "lightning arrester"
structed. It was then supposed that when a line was provided with a "lightning arrester " instruments would be "protected against lightning." This, however, did not prove to be the case; the discharges would sometimes pass to earth over the spark gap of the lightning arrester, but not infrequently would quite ignore the arrester and puncture the insulating material of the instruments, as before. In other words, the discharge was selective. The failure of the lightning arrester was a vexation, but at that time, owing to the small amount of apparatus in use, the damage, reckoned in dollars and cents, did not call for any special study of the reasons for the selective character of disruptive discharges. In these days, however, the vast amount of capital invested in electrical apparatus of various kinds, and the consequent increased annual loss, directly due to these disruptive discharges, has called for a thorough investigation of the subject and the designing of more effective means of protection.
It is a very significant fact that overhead wires, after being subjected to the influence of thunder storms, do not show the damage to insulation which one would ordinarily expect to find had the wires been actually struck by the lightning discharge. It is not uncommon, however, to hear of wires being "struck by lightning;' in fact, linemen will frequently volunteer to point out the exact spot where the lightning entered the wire. But, so far as I have been able to learn, overhead wires are not struck by lightning. The points usually selected by lightning discharges are discharges are trees, lightning rods, church steeples, tall chimneys, and the like. There seems to be no reason why lightning should strike a horizontal wire, particularly when insulated from the earth.
Overhead wires may become charged in three ways and combinations of these: By static induction from the clouds; by dynamic induction from a lightning discharge, and by conduction from the surrounding atmosphere. The writer inclines to the theory of conduction.
During thunder storms, and in many instances. during fair weather, the atmosphere becomes charged with electricity at a constantly increasing potential as we recede from the earth. At the top of Washington monument, Washington, D. C., a potential of 3,000 volts has been measured during thunder storms, and at the top of the Eiffel tower a potential of 10,000 volts has been measured. Now, it is well known that lightning is oscillatory. The first oscillation, or discharge, makes a crack or hole through the atmosphere, and through this the succeeding oscillations take place. About ten to twelve oscillations can be observed, and the time interval is reckoned at about .00001 of a second. The lightning, therefore, being oscillatory and the atmosphere charged, if an overhead wire be charged by conduction from the atmosphere-that is, become electrically a portion of it-then, with every lightning discharge it would seem as though the potential of the atmosphere would sympathize with the oscillatory character of the lightning, and that the charge in the atmosphere would also oscillate and produce oscillations in overhead wires, and, in fact, in all metallic conductors, such as wire fences, rails, etc. The fact that wires become heavily charged during fair weather offers further evidence that they are charged by conduction from the surrounding charged atmosphere. In some instances, lightning arresters have been known to discharge overhead wires at
the rate of 140 times a minute during perfectly fair weather.
In any case, whatever the method of charging may be, the discharges from overhead wires seem to be oscillatory, and during thunder storms they are, in most cases, simultaneous with lightning flashes.
If we raise one end of a trough of water, and then quickly lower it, the water will quietly surge back and forth. If when the water is returning we again raise the same end of the trough, a wave will be started forward which, meeting the returning wave, will combine or collide with it, causing a piling up of the water at that point. Further complications may be introduced by repeatedly, and at proper intervals, raising and lowering one end of the trough. If the crests of these waves be carefully examined, it will be noticed that they differ in height, and are constantly shifting their positions.
During thunder storms, the static electricity in overhead conductors surges back and forth very much as the water in a trough, and the indications are that electric waves are set up which combine and interfere with each other in such a manner as to produce frequent and unequally distributed points of high and low pressure. The ends of wires are points of reflection, and at these points the pressure is always great. Whatever may be the true explanation of the idiosyncrasies of disruptive discharges, it is, after all, with facts that we have to deal.
Referring to Fig. I, 1, let AA represent the terminals of a static induction machine; L, a battery of six one-half-gallon Leyden jars; B, a spark gap twelve thirty-seconds of an inch, and C1, C2, etc., variable spark gaps, and let the conditions be as