
Diffraction grating area 5 cm by 4.5 cm on 8 cm by 7.5 cm (approx) block of speculum metal
1905-05-26
1905-05-26
1894
1898
1881
1895-1909 (estimated)
1926, May
1910-1948 (estimated)
1795-1805
1783-1785
1747-1757
1745-1753
1899
1894
1882-1899
1882-1909 (estimated)
1926, April
1882, Nov 6
1756-1758
1840-1850
1745-1752
1954-1964
1753-1755
1845-1850
1934
1757-1761
1780-1820
1840-1850