The US Naval Observatory has processed several new collections related to the history of astronomy and exploration that are now available for research:
 
Transit of Venus Expeditions Collection (USNO sent expeditions in 1874 and 1882)
Hall Family Collection (Asaph Hall discovered the moons of Mars in 1877 at the Naval Observatory)
 
Additionally, the USNO has begun scanning their astronomical glass plate collection as well.
LS0430

"Construction of the Pennsylvania Ave. Subway, Philadelphia" Lantern slide used to illustrate an Engineering course on Railroads delivered by Samuel Tobias Wagner from 1895-1909 at the Wagner Free Institute of Science.