Loading and the loading coil
Q. What is the patent number for the original loading coil?
A. It is U.S. patent number 652,230 which you can view at the United States Patent Office: http://www.uspto.gov (external link) Physicist Michael Pupin's patent in 1900 caused almost as much controversy as Bell's telephone patents. As the crucial invention for extending long distance circuits it was an extremely valuable patent and hence contested by groups like AT&T which eventually bought the rights. It also served as an incentive for the Bell System to found Bell Labs. As Wasserman put it, AT&T had been "played to a virtual tie with a lone inventor working in an academic setting. . . This point was not ignored by management."
The definitive book on loading coil history and early long distance working is Neil Wasserman's book, From Invention to Innovation: Long Distance Telephone Transmission at The Turn of the Century. John Hopkins/AT&T Series in Telephone History. 1985.
