lamps much, do not notice this need, because we have accustomed ourselves to dispense with the capability, but persons who have not been so accustomed, do notice it There are two aspects under which this device may be examined. One is as an energysaving device, and the other as a convenience-giving device. If it is intended to employ it in a lamp on a 200-volt circuit, and limit with this device the amount of current which the lamp shall receive, so that it shall give sixteen candle-power and no more, that is one way of regarding the question. Or if you take a 100 volt lamp on a 10 volt circuit and simply desire to turn that lamp. low and obtain a reduced efficiency with the lamp in process, that is another way of looking at it. It is needless to say that the first method is certainly very advantageous, but very dangerous, because if the vibrator once fails, the lamp will be destroyed. The method particularly defined here is dimming a lamp. From some experiments with vibrating contacts of this description, I take it that the function of a vibrating contact of this kind is only in a minor degree in the resistance of the contact, as you would measure it when metal touches metal. Far the greater advantage lies in the time executed in free space by the spring, when out of contact with the point. It is obvious, that if you give a spring an amplitude of .1 of an inch, it cannot remain in communication with its contact point for more than a fraction of its period and only during that fraction can the voltage be maintained upon the lamp. It is for that very reason that the figures on page 441 give us no reasonable idea as to the relative amount of energy developed in the contact breaker or in the lamp. For example, take the last reading, .02 of an ampere and five volts on the voltmeter across the lamp. One might suppose from that at first sight, that the energy in the lamp was .1 of a watt and there was an energy of 105 volts, multiplied by .02 amperes or 2.1 watts in the contact breaker. That would be altogether, of course, incorrect. In the case of pulsating currents of this kind we can no longer rely on the ordinary multiplication of amperes and volts, because just at the time the current is active, the electromotive force is not active. All we can ascertain from these measurements is, that energy to the amount of the product of full supply pressure, and mean observed current is expended in the lamp and vibrator together. Now assuming that the value of this particular device is contained, for the present at least, in the dimming of the lamp, and its convenience to the public on that account, what we really want to know is, how long will it last. Can Mr. Moore tell us how long a vibrator, operated in this way, will keep at work? Will a vibrator last such a number of hours on trial as to justify the expectation, that the vibration will last the lifetime of a lamp? If there is anything in the paper that it is desirable to know it is that, and I have looked in vain for it in the paper. Probably the convenience of such an attachment would be very considerable if dimming could be effectually

gained, the only disadvantage being, that if anything goes wrong with the contact, you cannot get at it. It is in the vacuum. But let us hope that Mr. Moore has some knowledge that will enable him to give us information as to how long we may expect that contact to last.

MR. MOORE:-In accordance with the experiments that I have made, although I have been severely handicapped in this direction, the contacts have not shown appreciable wear. I have not made continuous runs of 600 or 800 hours. But I have placed the controller in circuit a day at a time, and three or four days in succession, but no change of any consequence occurred. It is a matter of great interest as to what further investigations will develop. As stated, the paper was written in the hope that it will cause further investigations to be made in this line, which evidently, according to good authority, has not been investigated, and is an unexplored field of great proportions, the exploration of which may be richly rewarded.

THE PRESIDENT:-I should think a difficulty would arise in the actual working of Fig. 3, on p. 441, where the vacuum of a lamp is utilized for the vacuum of the contacts. Here, as I understand, a contact screw passes through the chamber into the vacuum. From my experience with vacua, I should think you would find it difficult to obtain a working vacuum with anything movable entering into it. It might be done, though I question it. MR. MOORE:-Allow me to explain, Mr. President. The armature and contact only, are in the vacuum. The illustration is rather indistinct; but by carefully examining the same it will be noticed that the magnet is not within the vacuum, and therefore the regulating screw does not enter the vacuum.

DR. WILLIAM E. GEYER:-I think the paper in using the phrase varying-in-pressure contacts," implies that the regulation is in large part effected by a change in resistance, self-induction also coming in, and some of the gentlemen who have discussed the paper have assumed that it is largely a question of resistance. I think that is a mistake. As I understand it, this apparatus works not so much by any change in resistance or by self-induction coming in, as by the relative time that the contacts take place. Take for instance Fig. 2. The screw A is far to the left, so that the vibrating portion, B, strikes it only at the extreme end of its excursion. The contact is very short, and the current is on the lamp for just a moment. If the screw is turned further up, the current will last a longer time. The pressure will not be notably greater, and the current is on the lamp longer. When finally the screw is turned up very far, the contact will last for a considerable portion of the time of vibration, and the current is on longer still, and has a chance to heat the filament up. Of course, the time comes when the contact is continuous, and then the current has its full opportunity to heat up the filament. The rate of vibration, as I understand, would make no very particular

difference, because it is only the relative time of contact which counts. If the vibrations are twice as fast, there will be twice as many contacts. The only thing counting is the relative time of

contact.

THE PRESIDENT-I see a distinguished honorary member here. I would like to ask Mr. Preece to take a seat on the platform.

Gentlemen, you see there was wisdom in my having Mr. Moore's paper come in the beginning, for I felt quite sure that it would cause considerable discussion, which it has done, and I wanted to ensure full time for such discussion.

I will now give you a brief inaugural on the International Electrical Congress and World's Fair of 1893.

GENTLEMEN :-During the past few months a mighty human stream, daily increasing in volume, has continually flowed towards a single centre of population in the North American continent. This stream, fed from all parts of the earth, is formed by the many millions who are journeying toward the World's Fair, to do honor to those four hundred years' growth of the greatest Republic the world has ever seen.

Many of us have but recently left this mighty stream. Like others we visited Chicago to become eye-witnesses of the nation's growth. But not for this alone; perhaps the principal incentive to most of us has been a desire to take part in the International Electrical Congress of 1893, not only because we are especially interested in the progress of electrical science, but also because we are members of the AMERICAN INSTITUTE OF ELECTRICAL ENGINEERS, with whom the first conception of this Electrical Congress originated.

It has occured to me that in a brief inaugural address to the INSTITUTE, I could not select a better topic than the International Electrical Congress and World's Fair of 1893. I will, therefore, give you a few thoughts on this subject.

As in our journey we crossed the mighty continent, we saw on every side evidences of its vast mineral and agricultural wealth. As we passed through its populous cities and at last reached Chicago we wandered through its streets and examined with admiration the long rows of stately buildings. In all these things

we rejoiced at the growth of a nation that has achieved so much in so short a time. But was it not in that extra-mural, younger, but potentially greater Chicago, yclep'd "The Great White City," that we were most impressed? Its grandly proportioned buildings that arose as if by magic would have rendered a distant journey profitable, as a mere architectural display But when we crossed their portals and examined the rich exhibits, collected from all parts of the world, we rejoiced in these proofs both of the nation's and of the world's progress.

But the growth of the American Republic during the four hundred years that have passed since its discovery by the Genoese Navigator, marvellous as it has been, is less astonishing to us as electricians than the extraordinary development in that vigorous science, electricity, to which many of us have devoted the energies of our lives. Contrasting the World's Fair of Chicago, of 1893, which embraces exhibits in all departments of man's skill and industry, with the Philadelphia International Exhibition, of 1884, which, as you remember, was devoted wholly to electricity, I think will agree you with me that we have ample reason to rejoice at the progress made in the electrical field during the past nine years.

I have no sympathy with the unthinking critic who expresses disappointment with what he chooses to style the meagerness of the electrical display of the Chicago Exhibition. He probably estimates the value of an exhibit by the number of square feet of floor space it covers, rather than by its inherent possibilities. To my mind many exhibits whose actual demand for floor space are limited to less than one hundred square feet, would, were they estimated from the standpoint of their true value, demand more than the entire area of the exhibition grounds for their display.

Such critics fail to appreciate the fact that not in the Electricity Building alone, but throughout the entire exhibition as well, there is to be seen a grand display of the wonder working force of electricity. Almost countless arc and incandescent lights turn night into day, both in the buildings and over the extended areas outside them. Powerful search lights flash their bright beams far and wide beyond the gates of "The White City." Electric launches on the lagoons, and electric cars on the Intramural Railway show by actual practice the power electricity possesses in systems of transportation. Systems of telegraphic and