filar

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

According to Prof. Skeat it is derived from the Span. filigrana, from “filar, to spin, and grano, the grain or principal fibre of the material.”

Place the filar micrometer and the stage micrometer in their respective positions.

The method of observing which Brünnow employed was quite different from that of Struve, though the filar micrometer was used in both cases.

For several thousand years the stars have been called "fixed," but the fine rulings of the filar micrometer tell a different story.