Menlo Park: The World's First R&D Lab

The Incandescent Bulb
In October 1879, Edison changed world history by successfully passing current through a substance (in this case, a carbonized form of cardboard called Bristol board) that glowed without burning or melting. Other forms of light had already been created, but Edison's bulb was revolutionary in that it was practical: the first iteration, a replica of which is seen in the photo above, shone for 40 hours.

• Thomas Edison and the Making of America