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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