Here is one of Nikola Tesla's most important lectures; it brightened the world and everything in it. Of all these phenomena the most important to study' are the current phenomena on account of the already extensive and evergrowing use of currents for industrial purposes. It is now a century since the first practical source of current was produced and ever since the phenomena which accompany the flow of currents have been diligently studied and through the untiring efforts of scientific men the simple laws which govern them have been discovered. But these laws are found to hold good only when the currents are of a steady character. When the currents are rapidly varying in strength quite different phenomena often unexpected present themselves and quite different laws hold good which even now have not been determined as fully as is desirable though through the work principally of English scientists enough knowledge has been gained on the subject to enable us to treat simple cases which now present themselves in daily practice.