. Bell telephone magazine . r furtherresearch and development of this typeof cable for general undergrounduse. The following year, shortly be-fore Mr. Stone resigned, Mr. Hayestransferred responsibility for this re-search to Dr. George A. Campbell—who had joined his staff in the Fall of1897. Starting in February, 1899, Camp-bells approach quickly convinced himthat there would be substantial ad-vantages in concentrating on coilloading instead of continuous load-ing. Work on continuous loadingwas accordingly dropped, and a com-prehensive solution of the funda-mentally important problem of coilsp
. Bell telephone magazine . r furtherresearch and development of this typeof cable for general undergrounduse. The following year, shortly be-fore Mr. Stone resigned, Mr. Hayestransferred responsibility for this re-search to Dr. George A. Campbell—who had joined his staff in the Fall of1897. Starting in February, 1899, Camp-bells approach quickly convinced himthat there would be substantial ad-vantages in concentrating on coilloading instead of continuous load-ing. Work on continuous loadingwas accordingly dropped, and a com-prehensive solution of the funda-mentally important problem of coilspacing was soon reached. Histheory was experimentally verifiedin an extensive series of laboratorytests on reels of actual cable inSeptember, 1899. E. H. Colpittsassisted Campbell in these experi-ments, and subsequently made im-portant contributions in many otherphases of the development work. The development work which fol-lowed the 1899 laboratory tests cul-minated in successful installations of 1947 Hammond V. Hayes 163. A group of instrurnent inspectors and members of the Stock and Packing Department at I2J Purchase Street in i88g: G. K. Thotnpson, Frank Martin^ J. B. PFilkins, A. M. Dittmer, John Daly, J. W. 0Donnelly A. F. Hall experimental types of solenoidal air-core loading coils on two 24-mile ca-ble circuits in the Boston exchangearea, completed May 18, 1900, andon a 670-mile, 104-mil, open-wire linecompleted July 2, 1900. After anadequate test period, the experimen-tal loaded circuits were used in regu-lar commercial service for severalmonths. Shortly before the installation ofthe experimental cable loading, theparent Bell company learned thatProfessor M. I. Pupin, of ColumbiaUniversity, had independently workedout a theoretical solution of the coilloading problem. On June 19, 1900,two United States patents were is-sued to Professor Pupin. The con-flicting claims of the Pupin and Camp- bell applications resulted in extendedinterference proceedings which ended,on Ap
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