The Collaborative International Dictionary
Eriometer
Eriometer \E`ri*om"e*ter\, n. [Gr. ? wool + -meter.] (Opt.) An instrument for measuring the diameters of minute particles or fibers, from the size of the colored rings produced by the diffraction of the light in which the objects are viewed.
Wiktionary
eriometer
n. An optical device used to measure the diameters of fibres such as wool