Replica plane diffraction grating, area 23 x 23 mm, mounted on glass plate with label reading 'Thorp's Transparent Replica of Rowland / Metal Diffraction Grating / 14527 lines to the inch, in leathercloth-covered velvet-lined case.
Replica plane diffraction grating, area 23 x 23 mm, mounted on glass plate with label reading 'Thorp's Transparent Replica of Rowland / Metal Diffraction Grating / 14527 lines to the inch, in leathercloth-covered velvet-lined case.