eriometer

[Gr. erion =wool, and metron =a measure.] An instrument for measuring the diameter of small fibers, such as wool, cotton, or flax, by ascertaining the diameter of any one of the colored rings which they produce. "The eriometer is formed of a piece of card or plate of bra , having an aperture of about one-fiftieth of an inch in diameter in the center of a circle of one-half inch in diameter, and perforated with small holes. The fiber or particle to be measured is fixed in a slider, and the eriom eter being placed before a strong light, and the eye a isted by a lens applied behind the small hole, the rings of colors will be seen. The slider must then be drawn out or pushed in till the limit of the first red and green ring (the one selected by Dr. Young) coincides with the circle of perforations, and the index will then show on the scale the size of the particle or fiber." - Brewster: Optics.