While a definition for and usage history of "Let cooler heads prevail" can be both readily found, I have not been able to nail down the origins of the phrase. Ideas?
Learn English – “Cooler heads prevail” origin
etymologyidiomsphrase-origin
Related Solutions
The Phrase finder provides an explanation of the origin:
: To be under the weather is to be unwell. This comes again from a maritime source. In the old days, when a sailor was unwell, he was sent down below to help his recovery, under the deck and away from the weather.
... Here's a similar one I found: "Under the weather. To feel ill. Originally it meant to feel seasick or to be adversely affected by bad weather. The term is correctly 'under the weather bow' which is a gloomy prospect; the weather bow is the side upon which all the rotten weather is blowing." From "Salty Dog Talk: The Nautical Origins of Everyday Expressions" by Bill Beavis and Richard G. McCloskey (Sheridan House, Dobbs Ferry, N.Y., 1995. First published in Great Britain, 1983).
Another site states that something similar:
Passengers aboard ships become seasick most frequently during times of rough seas and bad weather. Seasickness is caused by the constant rocking motion of the ship. Sick passengers go below deck, which provides shelter from the weather, but just as importantly the sway is not as great below deck, low on the ship.
In both cases, we have two things in common. One, is its origin came from sea travel, when people felt ill due to several reasons, and the other thing in common, is that they both cited the fact that the persons feeling unwell went below deck.
Aeroplane factory slang
The earliest example I can find of the phrase pre-dates World War II, in the April 1938 edition of American Speech (Vol. 13, No. 2, pp. 155-157) in a list of "Aeroplane Factory English" by Edwin R. Coulson:
EGG IN YOUR BEER. An easy job; something for nothing.
A footnote says this "trade dialect" was collected at the Douglas Factory, Santa Monica, California.
Army slang
The October 1941 edition of American Speech (vol XVI, no 3) carried a "Glossary of Army Slang", including:
EGG IN YOUR BEER. Too much of a good thing.
The earliest military use I found was by PFC. George H. Willers of the US Marine Corps in a letter to Life magazine (8th September 1941):
Just what the hell do they want — eggs in their beer? The undersigned, a marine, "goes out to sea in ships" and is only too glad to get ashore once a month or so, even though it may not be these blessed shores, to places where the beer is lukewarm, where ice cream comes from a cow by way of a powdered-milk can, and the food in restaurants looks like it has been eaten before.
The American Heritage Dictionary of Idioms says:
This expression dates from about 1940 and became widespread during World War II. The origin is unknown, since adding egg to beer does not improve the taste.
A December 1946 American Speech (vol XXI, no 4) includes 'Army Speech in the European Theater’ by Joseph W. Bishop, Jr.:
“Whaddya want—an egg in your beer?" Properly, this is the retort courteous to a gripe, or bitch, which is not fully justified. By loose usage, it has become an answer to any and all complaints. I do not know its etymology, but my assumption has always been that it is based on the fact that fresh eggs and real beer were two of the scarcest desiderata in the ETO [European Theater of Operations], the possession of one of which ought to have sufficed any man. There is some evidence that it has been prevalent around Brooklyn for years, but at any rate it has had wider currency in the Army than ever before and has been more apt.”
Dewdroppers, Waldos, and Slackers: A Decade-by-Decade Guide to the Vanishing Vocabulary of the Twentieth Century (2003) by Rosemarie Ostler lists it under the forties:
egg in your beer: too much of a good thing. What do you want, egg in your beer? was a common retort to pointless or unjustified complaining since in the wartime world either an egg or a glass of beer alone should have been a sufficient luxury for anybody.
The Facts on File dictionary of clichés suggests it could be an aphrodisiac, and mentions an 1883 recipe containing egg white and mead, but says these rare recipes are probably unrelated to the saying, and that it "is presumably viewed as some kind of enrichment".
Eric Partridge's A Dictionary of Catch Phrases (1986):
what do you (or, illiterately yet frequently, whaddya) want? eggs (or an egg) in your beer? 'Usually said to be someone who is bitching or griping without justifiable cause. I have heard this used only by Marines, but I strongly suspect that it was borrowed from civilian use' (Col. Moe 1975). Therefore, tentatively: C20; civilian become, during WW2, Marine Corps.
'I heard this first in 1937, (as ...egg...) and in a civilian context. Certainly it has been in general (not just USMC) use since then' (R.C., 1978). A shorter var. is you want an egg in your beer?; cf what do you want? Jam on it?
Real egg in real beer
A preview from a (probable 1915) Catering industry employee: Volume 24 reports on a Seattle court case on whether egg-in-beer is food or a drink:
And:
EC Maddox, another witness for the city, asserted he paid a nickel and received an egg in his beer. On the stand, in his own behalf, Aronson averred that egg-in-beer is one of the oldest combinations known to mixologists.
Von Ziemssen's Handbook of General Therapeutics (1885) lists "Warm beer with egg" and Practical Druggist and Pharmaceutical Review of Reviews lists "Root Beer with Egg".
The Archives of Pediatrics (1916) says with surprise:
Other foods recommended were French bread, hashed meats, and, last but not least, small beer with egg yolks beaten in ! ! !
A 19th century The Pet-Stock, Pigeon, and Poultry Bulletin says:
It is an old-fashioned recipe to clear warm beer with egg shells, and coffee with the yelk of an egg, and the clearing properties of the yelk of an egg seems to have been known to the Romans...
So, who's going to test it out and crack an egg into their beer this weekend?
Best Answer
Antecedents of "cooler heads prevailed" go back at least to the early 1800s. For example, in a speech by the chancellor of the exchequer in connection with allegations of corruption involving the Duke of York, from "British and Foreign History for the Year 1809," chapter 2, in The New Annual Register, Or General Repository of History (July 1810):
As a set phrase, however, "cooler heads prevailed" seems to have emerged in the United States during the last quarter of the 1800s. Here are nine instances from the period 1876–1889, drawn from the results of Elephind, Hathi Trust, and Google Books searches.
From an untitled item in the [Jefferson City, Missouri] Sate Journal (August 4, 1876):
From "Fight with a Band of Thieves," in the Richmond [Virginia] Daily Dispatch (November 9, 1883):
From an untitled item in the San Antonio [Texas] Daily Light (October 23, 1884):
From "Natural Gas: The Agent of Great Destruction and Death in Pittsburg, PA.: Three Terrible Explosions Occur in Almost Immediate Succession," in the Wichita [Kansas] Daily Eagle (February 1, 1885):
From an untitled item in the Salt Lake [City, Utah] Evening Democrat (October 17, 1885):
From "History of Davies County," in History of Knox and Daviess Counties, Indiana (1886):
From John McMaster, Benjamin Franklin as a Man of Letters (1887):
From "A Fiend Incarnate," in the Coronado [California] Mercury (July 29, 1887):
From "The Faith Cure?" in the Los Angeles [California] Daily Herald (June 24, 1889):
The striking think about these U.S. instances of "cooler heads prevailed" is that virtually all of them involve situations where a riot or lynching seems imminent but is avoided when advocates of calm or the rule of law persuade an angry crowd not to become immediately violent. This is in sharp contrast to the 1810 instance from England, in which what prevails is not a nonviolent alternative to mob action, but a watered-down accusation of misconduct lodged in place of a more direct and forceful one.
The two earliest U.S. examples cited above—and five of the first six—use the form "the counsels [or advice or counsel] of cooler heads prevailed," which suggests that this was the original form of the expression. But the shorter form "cooler heads prevailed" appears in four of the nine instances, including one as early as 1884.
Today, "cooler heads prevailed" can apply to any situation where a more temperate action, response, or policy wins out over a less temperate one; but in its earliest manifestations in the United States, "cooler heads prevailed" seems to have been applied specifically to situations where mob violence was being incited by hotheads but was avoided through the intercession of calmer and wiser persons.