Grating, concave
1901
- Title
- Grating, concave
- Collection
- Caltech Images Collection
- Series
- Scientific Instrument Photographs
- Identifier
- ST-PH-09
- Dates
- 1901
- Extents
- 1 photographs (negative)
- Abstract
- 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.