[ New York, NY ]: Bell Telephone Laboratories, Inc. May 1951 and January 1955. First Separate Edition. Two items. Item One: Bell Telephone System Monograph 1841: "Single-frequency signaling system for long telephone trunks." 1-7, [1] (blank) pages. "Issued May, 1951" on inside rear cover. Some fading to grey covers, staple..... More