Washington, D.C., circa 1922. The second of two photos with the caption "William Armstrong Perry." National Photo Co. Collection glass negative. View full size.

Washington, D.C., circa 1922. "William Armstrong Perry." A former editor of Boys Life and Scouting magazines, W.A. Perry authored a study called "Radio in Education." National Photo Company Collection glass negative. View full size.

Washington, D.C., August 1923. "National Highways Association." An interesting variety of business machinery on display here including a Dictaphone and some Ediphone cylinders. National Photo Company glass negative. View full size.

March 21, 1938. Washington, D.C. "Purchasing on an average of 4 million electric light bulbs annually, Uncle Sam is probably one of the largest users of light in the country. The National Bureau of Standards sees that the government gets value received in purchases by continually testing the incandescent lamps to determine their life and the amount of light they give. Using a special machine designed by the Bureau, Louis Barbrow is shown measuring the amount of light given by a lamp." Harris & Ewing Collection glass negative. View full size.

Washington, D.C., circa 1919. "Chesapeake & Potomac Telephone Co. equipment." More communications gear at what seems to be the Capitol. The box on the left bears the nameplates of Leeds & Northrup, Philadelphia, and Western Electric. Harris & Ewing Collection glass negative. View full size | The knobs.

Washington, D.C., circa 1919. "Chesapeake & Potomac Telephone Co. switchboards." Harris & Ewing Collection glass negative. View full size.

Washington, D.C., circa 1919. "Chesapeake & Potomac Telephone Co. wiring." A behind the scenes look at communications tech some 80 years after the telegraph tapped out its first message. Harris & Ewing glass negative. View full size.

Washington, D.C., circa 1919. "Chesapeake & Potomac Telephone Co. equipment." Harris & Ewing Collection glass negative. View full size.