Transit Instrument, with reversing arrangement, illumination with oil or electric lamp, filar micrometer with two eye pieces.
In the filar micrometer two spider lines are parallel, and one intersects them at right angles.
Place the filar micrometer and the stage micrometer in their respective positions.
It can be used to measure the angular distance between objects too far apart for the filar micrometer.
(c) By means of the filar Micrometer (Ramsden's micrometer eyepiece).
To Bouguer in 1748 is due the true conception of measurement by double image without the auxiliary aid of a filar micrometer, viz.
filar fi·lar (fī'lər)
Relating to a thread or filament.
Composed of filaments or threadlike structures.