A common use of filar micrometers was measuring the distance between double stars.

A filar micrometer is a device used in astronomical telescopes for astrometry measurements.

He then measured carefully, with a filar micrometer, the apparent diameter of the planet now looming so large beneath them.

The precursor to the filar micrometer was the micrometer eyepiece, invented by William Gascoigne.

Being very difficult to measure, only about 60 stellar parallaxes had been obtained by the end of the 19th century, mostly by use of the filar micrometer.

Westfall, staring into the eyepiece of the filar micrometer, finished measuring the apparent size of the heptagon before he turned toward Stevens and Brandon.

Telescopes that are used for very precise measurements would have a filar micrometer as a reticle; this could be adjusted by the operator to measure angular distances between stars.

Pierre Bouguer, in 1748, originated the true conception of measurement by double image without the auxiliary aid of a filar micrometer, that is by changing the distance between two object-glasses of equal focus.

He inspected the power meters briefly, made several readings through the filar micrometer of number six visiplate, and checked the vernier readings of the great circles of the gyroscopes against the figures in his notebook.

Tammon was poring over a computed graph, measuring its various characteristics with vernier calipers, a filar microscope, and an integrating planimeter, when Mergon and Luloy came swinging hand in hand into his laboratory.

Although the heliometer was difficult to use, it had certain advantages for Bessel including a wider field of view compared to other great refractors of the period, and overcame atmospheric turbulence in measurements compared to a filar micrometer.