The first stop was a chat from our tour guide, who had to kill about twenty minutes in order for Jupiter to get up in the sky sufficiently to see it with the telescope. He talked about the history of time keeping at the USNO.
We walked over to the library-observatory building, where we passed this old 6" transit telescope. A transit telescope is unlike a regular telescope in that it is aligned onto a North-South axis. It is used to observe when stars cross the transit, thus allowing clocks to be adjusted.
The upper section of the USNO library, one of the finest collections of astronomical and timekeeping books in the world.
A watch on loan from the Smithsonian. I thought this was pretty cool. Presumably it has a standard watch face on the other side.
An old Ulysse-Nardin maritime chronometer. Like most such instruments, it sits in a box on a gimbaled mount to account for the wave motion aboard ship. We were also shown an astrolabe.
The 12" telescope in the observatory dome that we used to observe Jupiter. That's the eyepiece at left; you have to climb a ladder to view through the telescope.