DR. GEORGE A. CAMPBELL 557 



the more outstanding of Dr. Campbell's contributions to the art of 

 electrical communication as they fit into the history of that art. 

 Their diversity is such as to establish the unusual versatility of Camp- 

 bell's genius. His is a career unusually productive of discoveries, 

 inventions and patents. Many of his important memoranda, however, 

 were never worked up in the detailed form which would render them 

 suitable for publication, and still reside only in the Company's engi- 

 neering files. It would be regrettable to pass this occasion by without 

 some notice being taken of these unpublished documents, and perhaps 

 as fitting a commemoration as any is to print a few of the briefer ones 

 just as they were written. Choosing somewhat at random, we are 

 selecting the above cited memorandum of March 7, 1912, in which 

 the 22-type repeater and the four-wire circuit are suggested, and 

 two memoranda of earlier dates discussing capacity unbalances and 

 crosstalk. The memorandum on repeaters is perhaps particularly 

 interesting because of its historical flavor. Written twenty-three 

 years ago, it refers to the measurement of attenuation in miles of 

 cable, not decibels, and to such considerations as the natural period 

 of the mechanical repeater diaphragm. 



