"The first great law of our prophet," said he to the people, "is a law of freedom.
— from Life of Schamyl And Narrative of the Circassian War of Independence Against Russia by J. Milton (John Milton) Mackie

When the brush discharge is observed in air at the positive and negative surfaces, there is a very remarkable difference, the true and full comprehension of which would, no doubt, be of the utmost importance to the physics of electricity; it would throw great light on our present subject, i.e. the molecular action of dielectrics under induction, and its consequences; and seems very open to, and accessible by, experimental inquiry.
— from Experimental Researches in Electricity, Volume 1 by Michael Faraday

2. Of nouns in um , some have no need of the plural; as, bdellium, decorum, elysium, equilibrium, guaiacum, laudanum, odium, opium, petroleum, serum, viaticum .
— from The Grammar of English Grammars by Goold Brown