This object is not on display at the National Air and Space Museum. It is either on loan or in storage.
Collection Item Summary:
This is a filar micrometer, likely made by Brashear of Pittsburgh, and used visually on the 24 inch refractor of the Sproul Observatory, Swarthmore College since its opening in 1913. It contains tiny electrical lamps, and some later modifications. Designed by Klages of Brashear, it connects to telescope by bayonet mount. Filar micrometers were precursors for double star positional astronomy and astrometry prior to the photographic era.
Swarthmore College donated this set of objects to the Museum in 2017.