Via Shorpy: "Washington, D.C., 1927. No caption on this Harris & Ewing glass plate of what seems to be facsimile equipment. "
Mark Frauenfelder is the founder of Boing Boing and the editor-in-chief of MAKE and Cool Tools. Twitter: @frauenfelder. His new book is Maker Dad: Lunch Box Guitars, Antigravity Jars, and 22 Other Incredibly Cool Father-Daughter DIY Projects