Direct vision grating pocket microscope with adjustable slit made by T. Thorp, Manchester, with case, 1890-1900. Direct vision grating pocket microscope with adjustable slit 1890-1900
Replica plane diffraction grating, area 49 x 36 mm, mounted on glass plate with label reading 'Thorp's Transparent Replica of Rowland's / Metal Diffraction Grating / 14505 lines to the inch', and with 'The original is the property of Dr Common / Thomas Thorp / Whitefield [ . . . . ] / Oct 1906' [one word is indecipherable: reading of the year is also uncertain] written in white ink on the black edging tape. Replica plane diffraction grating 1906, October