And there was a marker for Joseph Henry. People that work with electronics all know the "henry" as a unit of measure. For instance, consider this vacuum tube electronics fan's excitement after installing a 3 henry choke!
But after reading the Wikipedia entry for Henry, I now know his major contribution to electricity wasn't just measurement.
He was the first to coil insulated wire tightly around an iron core in order to make a more powerful electromagnet, improving on William Sturgeon's electromagnet which used loosely coiled uninsulated wire.OK, probably not as exciting as visiting that Big Gun museum.