Demainbray's convex lens
1750
1750
1720
circa 1750
1742
2000-100 BCE
1705-1737
1725
1735-1745
1720
1745
1730
1990-96
1720-1730
4000-2001 BCE
1725
1725
1730-1750
1725
10000-5000 BCE
1910-130
1730-1736
1740
1744
1736-1740
1740
1713-1750
1750
1738
1730
1745
1730
1737-1738
1750
1743
1737
1720
1732
1747
1750
1740
1750
1746
1692-1730
1730
1718
1730
1737
1940-1050
1746
1748