The reslilts are given of about one hundred series of tests, each covering a range in frequency up to about 5000 cycles per second, on the impedance of long loops of parallel conductors of different metals, sizes, and cross-sectional forms. The measuring apparatus is detailed. The theory of the skin effect in solid rods and in indefinitely wide flat strips is appended in a new and simplified form. THE FOLLOWING researches were conducted, under an appropriation from the American Telephone and Telegraph Co., at the Massachusetts Institute of Technology in the Research Division of the Electrical Engineering Department, during the year 1914-15. In the early part of 1914, they were carried on under the directorship of Prof. Harold Pender. They date their origin, however, to M. I. T. thesis work undertaken in 1912-13. Brief Early Historical Outline of Skin Effect Research. The first mathematical discussion of auto-distorted alternatingcurrent density in a wire appears to have been given by Maxwell in 1873. Heaviside contributed an extensive mathematical literature to the whole subject in 1884-1887. J. H. Poynting also contributed to the mathematics of the subject in 1884-1885. Hughes developed the experimental side of the subject in 1886. Lord Rayleigh in 1886 first gave the formula for skin effect in an infinitely wide strip. Dr. H. F. Weber in 1886, J. Stefan in 1887 and 0. Lodge in 1888 contributed further material. Lord Kelvin gave the expression in ber-bei functions in 1889. Hertz in 1889 and Sir J. J. Thomson in 1893 discussed the subject both from the experimental and mathematical standpoints. Mr. J. Swinburne used the term " skin-effect " in 1891.1
The reslilts are given of about one hundred series of tests, each covering a range in frequency up to about 5000 cycles per second, on the impedance of long loops of parallel conductors of different metals, sizes, and cross-sectional forms. The measuring apparatus is detailed. The theory of the skin effect in solid rods and in indefinitely wide flat strips is appended in a new and simplified form. THE FOLLOWING researches were conducted, under an appropriation from the American Telephone and Telegraph Co., at the Massachusetts Institute of Technology in the Research Division of the Electrical Engineering Department, during the year 1914-15. In the early part of 1914, they were carried on under the directorship of Prof. Harold Pender. They date their origin, however, to M. I. T. thesis work undertaken in 1912-13. Brief Early Historical Outline of Skin Effect Research. The first mathematical discussion of auto-distorted alternatingcurrent density in a wire appears to have been given by Maxwell in 1873. Heaviside contributed an extensive mathematical literature to the whole subject in 1884-1887. J. H. Poynting also contributed to the mathematics of the subject in 1884-1885. Hughes developed the experimental side of the subject in 1886. Lord Rayleigh in 1886 first gave the formula for skin effect in an infinitely wide strip. Dr. H. F. Weber in 1886, J. Stefan in 1887 and 0. Lodge in 1888 contributed further material. Lord Kelvin gave the expression in ber-bei functions in 1889. Hertz in 1889 and Sir J. J. Thomson in 1893 discussed the subject both from the experimental and mathematical standpoints. Mr. J. Swinburne used the term " skin-effect " in 1891.1
THE CHAIRMAN [W. J. Hammer]:-The Chair wishes to an-nounee that at the meeting of the Couneil this afternoon the certificate of membership whieh, doubtless, you have all seen in the adjoini'ng room, was adopted with one or two slight changes., This certificate will be issued to full members onily. It will be a comipliment fromn the Institute to those wlio have attained a high rank professionally, and whose work in their profession and for the Institute entitles thein to receiv7e it. These certificates. will probably be ready within two or three weeks and. will be printed upon heavy parchrnrent paper at abont cost, namely, one dollar. The Secretary has beern instrutcted to send out a notice, stating the conditions under which this certificate is givenl and other matters pertainiing thereto, as soon as they are ready for distribution. rThe American Institute of Electrical Engineers desires to raise its status as a scientific organization in every way possible, and it is believed that by issuing this certificate to full members only, the honor conferred will be more highly appreciated and it will result in a desire upon the part of many of our associate inembers to apply for and to secure full membership in the Institute. While in soine of the engineering societies the majority of the members are active or full members, and there are comiparatively few associate metm)bers, in the Institute of Electrical ETngineers the opposite is the easy, and the issuing of this certificate under the cornditions as recommended by the Special Commnittee will prove advantageous to the interests of the Institute as well as to the miembers receiving the saine.
IyRNNELLV, AcnAkn, AND DANA .[J . F . I, 110 .07 metres) in length, ranging in linear mass from 6o to 100 pounds avoirdupois per yard (30 to 3o kilogrannnes per metre) . with corresponding cross-sections from 6 to io square inches (3 8 . 5 to 64 .5 square centimetres) . The cross-sections of these rails are represented to scale in Figs . 5 to to .Frequencies and Strengths o f Alternating Testing Current .-Three frequencies have been used in the tests ; namely, 25, 45, and 6o cycles per second . The bulk of the work was, however, carried on at or near two frequencies only ; i.e ., 25 and 6o cycles per second .The current-strengths employed in the test rails varied from io to Boo amperes r . m . s .Diagram of test circuit.Auk., 1916 .1 SKIN I"I'RLCT IS `;TEEF. 1y .AJLS_ the ground on brick pillars .1 he rest of the rectangular loop BCDEFA was composed of straight copper conductors (wire or cable) . The extensions Alt and BC: from the ends of the rail were made so as to enable the electro-niagnetic field in the neighborhood to be both more nearly uniform and more readily calculated . The circuit was erected in an alley between two brick buildings, remote from iron . A photograph of the rail in position appears in Fig . 2 .Fln. 2, Rail m p'naion tot test .Sources of Alternating-current Supply .-For the frequency of 25 eo, a General Electric 3-phase 5o-kva . alternator, 6-pole 514 r . p . m .-230 volts-i26 amperes was used . For the frequency of 6o w , a Mordey single-phase, 4o-kva. alternator was used, with 9 poles and 9 pancake coils, for supplying about 135 amperes r. m . s ., at about 300 volts . The arrangement of circuits used is shown in Fig . 3 . The transformer T was a General Electric Company's r5-kva ., 6o N, single-phase transformer from 22o to t8 volts . The secondary terminals were connected directly to the test circuit through two four-terminal manganin resistors, and the
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