DESCRIPTION:
This is an eyepiece with a wheel of 9 different grids, numbered 1 through 9 on the grids themselves; grid 4 is shown to the left. The top of the eyepiece is in a sleeve allowing the user to accurately focus on the grids without affecting the focus on the specimen. The eyepiece has a knob to fix it on the optical tube of the microscope so it does not rotate within the tube. It comes in a leather-covered case lined with blue velour. The case has the B & L insignia on top. The eyepiece is signed EYEPIECE FOR, GRAIN SIZE, DETERMINATION with the B & L insignia under that and under that BAUSCH, & LOMB, OPT. CO., U.S.A.

CONDITION:
The condition of the case and eyepiece are cosmetically excellent. Some of the grids are worn, a few completely worn, and some numbers are not visible. It is still quite usable with most of the grids.

HISTORY AND PURPOSE
This is an eyepiece designed for use in metallurgy. It was used to determine grain size of iron-containing metals. Since these are opaque specimens, this eyepiece would be used with a vertical illuminator or a metallurgical microscope equipped for vertical illumination. The grain size is an important characteristic of metals which may affect rigidity and elasticity. Grain size is a term related to density of grains per square inch: