result, if we judge from the effect which our simple rules of election produced. I think no matter how we define anything, in very many minds it will tend to ambiguity. I admit very freely the force of your reasoning, and in my own mind I have gone through it all. The poles of the magnet which point to the terrestrial north or south, might be called-as attempts have been made to call them from almost time immemorial-the north seeking pole, or the south seeking pole, or the blue or red poles, or the austral and boreal poles, etc. I imagined that the Committee had taken those points into consideration, and had come to the conclusion that no matter what we officially name the magnet poles, we shall continue to call the north pole of the earth the north pole, no matter where the needle points, and although the majority of us know, or think we know, much better. we will persist in calling that point of the needle, which points northward, the north pole. My suggested amendment was simply to the Committee's definition, and in view of the fact that I supposed they had taken all these matters into consideration, I did not feel myself authorized to go any further into that, but simply to give one of the suggestions which had been called for. THE PRESIDENT:-I may be wrong, but I think the general practice in this country is to call the end of the needle which points approximately to the earth's north, north, and to regard the magnetism of the Northern Hemisphere of the earth, as essentially south. That, I think, is the general idea that is held now. MR. LOCKWOOD:-If that be the case, it is one of the instances where the smaller governs the greater. I do not suppose that any number of needles will govern the polarity of the earth. But I can imagine that the polarity of the earth will tend, in some degree at least, to direct the needle. I do not think that the terminology which we apply to the polarity of the earth should govern the terminology which we apply to the polarity of the needle. I should like to hear what the views of the Commitee were, if any of the members of the Committee will kindly give them. MR. KENNELLY:-The Committee endeavored to enunciate the very statement that the President has just given us, and the amendment that Mr. Lockwood has offered I take to be intended for the benefit of those unhappy creatures whose lot might be cast between the north geographic pole and the magnetic pole in its vicinity, and who, of course, contrary to the definition of the Institute's Committee, would find the magnetic pole geographically south, as they would live north of it. But if we eliminate that section of our planet, which is fortunately rather remote, the suggestion of the Committee will practically agree with the suggestion that I understood Mr. Lockwood's amendment to improve, namely, that the magnetic pole of the earth which is ter restrially north, or situated in the vicinity of the geographic north pole shall be the earth's south magnetic pole, and that the pole of a needle which points toward it when allowed to assume its natural direction, shall be the north pole of that needle. THE SECRETARY:-In regard to this final closing up of the work of the Committee preparatory to the assembling of the Electrical Congress, it is probable that this will be the last meeting of the INSTITUTE before the convening of that Congress, and therefore it would be proper to suggest that this final summing up be published, either in the TRANSACTIONS or in the electrical journals or both, before the regular meetings of the INSTITUTE, in order to have it in general circulation before the Congress. As we are not prepared to close it up at present, and it appears to me that authority should be given for that to be done without further discussion of the matter before the INSTITUTE, I would make a motion to the effect that the Sub-Committee on Provisional Programme be authorized, at such time as they find convenient before the assembling of the Congress, to publish, through the electrical journals and the TRANSACTIONS, such a summing up as they may deem proper. The motion was seconded by Mr. Hammer and carried. ing of the American Institute of Electrical Engineers, Columbia College, New York, May 17, 1893. President Houston in the Chair. PRACTICAL ASPECTS OF LOW FREQUENCY ELECTRICAL RESONANCE. BY M. I. PUPIN, PH. D., COLUMBIA COLLEGE. Mr. President and Gentlemen of the Institute:-A large part of the subject of the following discourse was discussed by me, but in a different way, in three papers. Two of these appeared in the April and May numbers of the American Journal of Science. The third will appear in the June number of the same journal. The method which I have adopted in the following discussion seemed preferable to the mathematical method which I followed in those papers. It is probably just as exact, and certainly a much clearer way of viewing the variable flow of electricity, especially those features of it, which have a more or less direct practical bearing. 1. ON THE NATURAL PERIOD OF AN ELECTRICAL CIRCUIT. An electrical circuit possessing self-induction and capacity behaves in a great many respects as a body does in consequence of its inertia and elasticity. The fundamental reason for this analogy is simply this:-The electromagnetic energy of a coil through which a current flows, has all the characteristic properties of the kinetic energy of a moving body, whereas the energy of the static charge of a condenser has all the characteristic properties of the potential energy of a strained elastic body. If the neutral state of such an electrical circuit is disturbed, it will return to it again after performing a certain number of oscillations about the position of its neutral state. But a return to the neutral state is impossible until the energy which is spent upon the circuit to disturb its neutral state has left the circuit, or to use a more technical expression, until the energy has been dissi pated or given off to some other circuit. The two principal causes which produce dissipation and compel the circuit to return to its neutral state again, are frictional resistances and radiation. Just as in the case of vibrating bodies, so also in the case of electrical oscillations, losses due to radiation, especially when no other electrical circuits are near, are exceedingly small when the oscillations are slow. In Herzian oscillations they are quite considerable. In oscillations of the Tesla frequency they are probably not negligible. My remarks refer to electrical oscillations of long period, therefore losses due to frictional resistances are the only losses which I shall consider. Consider now an electrical circuit consisting of a coil A and a condenser B (Fig. 1) in series with it. It is a circuit with localized self-induction and capacity. I trust that my discussion will lose as little in its generality as it will in its practical bearing if I confine it to such circuits only. B Let a sudden electrical impulse disturb the neutral state of this circuit; electrical oscillations will result. These oscillations follow laws practically identical with the laws of the motion of a slowly vibrating body. Their period is constant, as we all know, and it is in general completely determined by the electromagnetic moment of inertia and the dielectric elasticity of the circuit-that is, by its coefficient of self-induction and its capacity. When, however, frictional losses due to ohmic resistance, magnetic and dielectric hysteresis are large, then the period of this circuit is no longer defined by the self-induction and capacity alone, but it is also influenced by these frictional losses. When ohmic resistance and hysteresis losses are small enough, then the natural period of the circuit is given by the well-known formula Current Where is the natural period of the circuit in seconds, L its coefficient of self-induction in henrys, and C its capacity in microfarads. For instance, a large Bell telephone whose coefficient of self-induction is 0.5 henrys when connected in series to a condenser of 1 microfarad capacity will have a natural period of very nearly seconds, that is to say, an electrical disturbance would set up oscillations in it, 225 of which would take place in one second. If a permanent magnet were brought into the vicinity of the telephone coil and then suddenly removed, the telephone would sing a note whose pitch would be a little below the well-known note C. But it would not sing it very long. For since the ohmic resistance is 100 ohms these oscillations would disappear almost entirely after 3 5 <-10 Time in the of a second FIG. 2. 10 complete oscillations, somewhat in the manner represented in diagram Fig. 2, that is to say the telephone would sing only during about part of a second. By diminishing the resistance we could prolong its song. But diminish the resistance as much as you please, the pitch of the note of the telephone will remain the same, because, as I said, the natural period of the telephone circuit just described is within wide limits independent of the ohmic resistance. 2. ON THE TUNING OF AN ELECTRICAL CIRCUIT. To change the note, say to make it higher, it would be necessary to diminish the capacity of the condenser. When a piano tuner wishes to raise the pitch of a piano string he gives it more |