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INVENTIONS OF NIKOLA TESLA.

been discovered. But these laws are found to hold good onlywhen the currents are of a steady character. When the currentsare rapidly varying in strength, quite different phenomena, oftenunexpected, present themselves, and quite different laws holdgood, which even now have not been determined as fully as isdesirable, though through the work, principally, of English scien-tists, enough knowledge has been gained on the subject to enableus to treat simple cases which now present themselves in dailypractice.

The phenomena which are peculiar to the changing characterof the currents are greatly exalted when the rate of change isincreased, hence the study of these currents is considerably facil-itated by the employment of properly constructed apparatus.It was with this and other objects in view that I constructedalternate current machines capable of giving more than twomillion reversals of current per minute, and to this circumstanceit is principally due, that I am able to bring to your attentionsome of the results thus far reached, which I hope will prove tobe a step in advance on account, of their direct bearing upon oneof the most important problems, namely, the production of apractical and efficient source of light.

The study of such rapidly alternating currents is very interest-ing. Nearly every experiment discloses something new. Manyresults may, of course, be predicted, but many more are unfore-seen. The experimenter makes many interesting observations.For instance, we take a piece of iron and hold it against a magnet.Starting from low alternations and running up higher and higherwe feel the impulses succeed each other faster and faster, getweaker and weaker, and finally disappear. We then observe acontinuous pull; the pull, of course, is not continuous; it onlyappears so to us; our sense of touch is imperfect.

We may next establish an arc between the electrodes andobserve, as the alternations rise, that the note which accompaniesalternating arcs gets shriller and shriller, gradually weakens, andfinally ceases. The air vibrations, of course, continue, but theyare too weak to be perceived; our sense of hearing fails us.

We observe the small physiological effects, the rapid heating ofthe iron cores and conductors, curious inductive effects, interest-ing condenser phenomena, and still more interesting light phe-nomena with a high tension induction coil. All these experi-ments and observations would be of the greatest interest to the