Title: Grating, concave
Date: 1901
Original Format: photograph: negative
Description: This grating was ruled on speculum; a light aluminum coat has since been applied. The plate was prepared by the John A. Brashear Co., Allegheny, PA. It was ruled on Prof. Henry Rowland’s engine at Johns Hopkins Univ., Baltimore, MD. Used by Bowen and Millikan from 1919 on.
Collection: Scientific Instruments
Caltech Archives ID: ST-PH-09
