The first item is Jack Daniel's "cup and stem" (hydrometer). It was used to accurately determine proof of spirits. It was patented on October 16, 1866. It was bought by Jack Daniel and calibrated by the Internal Revenue Department in 1885.
The first picture is Mr. Lant Wood sampling the whiskey in the late 1940's or early 1950's. This hydrometer is sitting on the barrel.
The rest of the pictures are of the hydrometer itself.