In 1750 the British Royal Society received a curious report titled Lucina Sine Concubita, which translated means "Pregnancy without Intercourse".

In the letter the writer argued that women could become pregnant without having engaged in any sexual activity, due to the presence of microscopic "floating animalcula" present in the air. The author claimed to have isolated some of these animalcula using "a wonderful, cylindrical, catoptrical, rotundo-concavo-convex machine." When he examined these animalcula under a microscope he found them to be shaped like miniature men and women. This discovery, he suggested, would go a long way toward restoring the honor of women who could not otherwise explain their pregnancies. An engraving accompanying the letter showed a "floating animalcula" approaching a sleeping woman.

The author concluded by proposing that, for the purpose of experimentation, a royal edict should ban copulation for one year.

The letter was signed by Abraham Johnson, but this was a pseudonym of Sir John Hill. His intent was apparently to satirize the "spermist" theory, which held that sperm were actually little men (homunculi) that, when placed inside women, grew into children.

The letter proved very popular and was printed and distributed widely throughout Europe.

It is also said that Hill wrote the letter to revenge himself for having been denied membership to the Royal Society. (Needs confirmation)