It was the heat, the awful heat. Sailors from temperate climes who were transported into the tropics sometimes suffered a heatstroke, called a calenture, that resulted in temporary insanity. The tale used to be told that weeks of being becalmed in the Doldrums led afflicted sailors to imagine the sea to be the cool green fields of home and that they would try to reach it by jumping overboard.
So, by a calenture misled,
The mariner with rapture sees,
On the smooth ocean’s azure bed,
Enamelled fields and verdant trees:
With eager haste he longs to rove
In that fantastic scene, and thinks
It must be some enchanted grove;
And in he leaps, and down he sinks.
The Bubble, by Jonathan Swift, 1721, a satirical poem about the infamous speculative South Sea Bubble of that year.
The word comes from Spanish calentura, a fever or sunstroke, based on the Latin verb calere, to be warm. A less fanciful description comes from two decades after Swift’s poem:
Having heard so often of a Calenture, I expected to meet with some instances of it, even before I arrived in the West-Indies; but they are now grown very scarce, for I never saw above one person labouring under it: He was continuously laughing, and if I may be indulged in the term, merrily mad: One day in the height of his frenzy, he jumped over-board in Charles-Town Bay, but was luckily saved from drowning by one of his Sailors, or from being devoured by same ravenous Shark.
A Natural History of Nevis, by William Smith, 1745.
The word may well be familiar from two famous eighteenth-century seafaring works: Swift’s Gulliver’s Travels and Defoe’s Robinson Crusoe. Later, a calenture became any kind of raging fever linked to delirium and it also took on a figurative sense of some burning passion, the feverish ardour of a man afflicted with love, or the emotions of a spurned lover:
That the man who had promised to marry her, had exhausted the vocabulary of love for her, should thus cast her off, struck her into a frantic calenture which, for a season, threatened her existence.
The Spinners, by Eden Phillpotts, 1918.