CONTRIBUTORS TO THIS ISSUE 637 



ment, Bell Telephone Laboratories, 191 3-. Mr. Hartley is in charge 

 of researches in the field of carrier current, telephone repeater, and 

 telegraph systems. 



H. A. Affel, S.B. in Electrical Engineering, Massachusetts Institute 

 of Technology, 1914; research assistant in electrical engineering, 1914- 

 16; Engineering Department and the Department of Development 

 and Research, American Telephone and Telegraph Company, 19 16-. 

 Mr. Affel has been engaged chiefly in development work connected 

 with carrier telephone and telegraph systems. 



Charles S. Demarest, E.E., University of Minnesota, 1911 ; Amer- 

 ican Telephone and Telegraph Company, Engineering Department, 

 1911-19; Department of Development and Research, 1919-. Mr. 

 Demarest's work has been connected with the development of equip- 

 ment for toll telephone systems, including that for long distance cables, 

 carrier and radio systems. 



C.W. Green, B.S. in Electrical Engineering,University of Wisconsin, 

 1907; instructor and assistant professor, Massachusetts Institute of 

 Technology, 1907-17; captain 1917, major 1918, U. S. Army; Bell 

 Telephone Laboratories, 1919-. Mr. Green's work has had to do with 

 the development of carrier telephone systems and voice frequency 

 repeaters. 



