1827 introductions

In chemistry, isomers are molecules or polyatomic ions with an identical molecular formula – that is, the same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism refers to the existence or possibility of isomers.

Solresol (Solfège: Sol-Re-Sol), originally called (lit. 'Universal language') and then ('Universal musical language'), is a musical constructed language devised by French music teacher and composer Jean-François Sudre (1787–1862), beginning in 1817. His book defining it, , was published posthumously in 1866, though he had already been publicizing it for some years. Solresol enjoyed a brief spell of popularity in the latter half of the century and was sponsored by such figures as Victor Hugo, Alphonse de Lamartine, Alexander von Humboldt and Napoleon III, culminating with Boleslas Gajewski's pu

skirt worn in ballet by women

first stage and age of the Upper Jurassic series / Late Jurassic epoch

written work by naturalist and painter John James Audubon

eyeglass lens with three distinct optical powers