The year self-educated Peter Barlow published An Elementary Investigation of the Theory of Numbers. He commented that 230(231 - 1) is the greatest perfect number that will ever be discovered, for, as they are merely curious without being useful, it is not likely that any person will attempt to find one beyond it. Quoted in Conic Sections (Dublin 1993).
Chang and Eng, the most famous set of "Siamese twins," were born in Siam (modern day Thailand) in 1811.
The year Italian physicist and lawyer Amedeo Avogrado first determined the volume of one mole of a gas. [Tittle]
The Saros cycle is approximately 18 years, 11 days long. [NASA]