The phrase gaiety of nations means: enjoyment or pleasure shared by a large number of people.

This phrase occurs, for example, in Cometh the flower, by Christine Manby, published in The Independent (London, England) of Monday 14^th February 2022:

Fourteenth of February is also National Ferris Wheel Day in the United States, with people (at least five of them, I’m sure) taking the time to celebrate the birth of George Washington Gale Ferris, who invented the eponymous ride in 1893. Feriss’s original wheel, designed to rival the Eiffel Tower, harnessed the new-fangled power of electricity and debuted at the World’s Columbian Exposition in Chicago. The wheel was a huge success. Alas Ferris himself came to a sad end: divorced, bankrupt and dead of typhoid at the tender age of 37. Bearing all that in mind, it seems only right to spend a day queueing for the London Eye in recognition of Ferris’s contribution to the gaiety of nations.

The phrase gaiety of nations was coined by the English author and lexicographer Samuel Johnson (1709-1784) in Smith ¹, published in Prefaces, biographical and critical, to the works of the English poets (London: Printed by J. Nichols; for C. Bathurst, J. Buckland, W. Strahan, J. Rivington and Sons, [&c.], 1779):

At this man’s ² table I enjoyed many chearful and instructive hours, with companions such as are not often found; with one who has lengthened, and one who has gladdened life; with Dr. James, whose skill in physick will be long remembered; and with David Garrick ³, whom I hoped to have gratified with this character of our common friend: but what are the hopes of man! I am disappointed by that stroke of death, which has eclipsed the gaiety of nations, and impoverished the publick stock of harmless pleasure.

¹ Edmund Smith (born Edmund Neale – 1672-1710) was an English poet.
² Gilbert Walmsley (1680-1751) was an English barrister.
³ David Garrick (1717-1779) was an English actor, playwright and theatre manager.

A person signing themself ‘B. S. R.’ criticised Samuel Johnson’s metaphors in a letter to the Editor, published in The Westminster Magazine (London, England) of November 1779:

“But what are the hopes of man! I am disappointed by that stroke of death which has eclipsed the gaiety of nations, and impoverished the publick stock of harmless pleasure.” The faultiness of the metaphor is too gross to be insisted on. “A stroke eclipses!” Risum teneatis ⁴? But what is the consequence of Garrick’s death? Why, it has eclipsed the gaiety of nations. That this circumstance may have reached France, I am willing to allow; that it may have found its way into Italy may be perhaps admitted; but I must deny its ever having entered Chili: nor can I think that the Mahometan ever laid aside his opiate, or his terrestrial Houris to express the poignancy of his sorrow; or that the wild Irishman, or wilder North American, ever set up their funeral howl: nay, I have the authority of a great traveller, when I assert that there are several villages and small towns in a remote country called Albion, which never heard of Garrick whilst he lived, or wept when he died.

⁴ This refers to the following passage from Ars Poetica (The Art of Poetry), by the Roman poet Horace (Quintus Horatius Flaccus – 65-8 BC):

Spectatum admissi risum teneatis, amici?
     translation:
If you were admitted to such a sight, could you refrain from laughter, my friends?

In The Life of Samuel Johnson, LL. D. (London: Printed by Henry Baldwin, for Charles Dilly, 1791), the Scottish biographer James Boswell (1740-1795) recalled asking Samuel Johnson to explain his metaphors during a conversation which took place on Saturday 24^th April 1779 at Mr. Beauclerk’s:

I presumed to animadvert on his eulogy on Garrick, in his “Lives of the Poets.” “You say, Sir, his death eclipsed the gaiety of nations.” Johnson. “I could not have said more nor less. It is the truth; eclipsed, not extinguished; and his death did eclipse; it was like a storm.” Boswell. “But why nations? Did his gaiety extend farther than his own nation?” Johnson. “Why, Sir, some exaggeration must be allowed. Besides, nations may be said if we allow the Scotch to be a nation, and to have gaiety, which they have not. You are an exception though. Come, gentlemen, let us candidly admit that there is one Scotchman who is cheerful.” Beauclerk. “But he is a very unnatural Scotchman.” I, however, continued to think the compliment to Garrick hyperbolically untrue. His acting had ceased some time before his death; at any rate he had acted in Ireland but a short time, at an early period of his life, and never in Scotland. I objected also to what appears an anticlimax of praise, when contrasted with the preceding panegyrick—“and diminished the publick stock of harmless pleasure!”—“Is not harmless pleasure very tame?” Johnson. “Nay, Sir, harmless pleasure is the highest praise. Pleasure is a word of dubious import; pleasure is in general dangerous, and pernicious to virtue; to be able therefore to furnish pleasure that is harmless, pleasure pure and unalloyed, is as great a power as man can possess.” This was, perhaps, as ingenious a defence as could be made; still, however, I was not satisfied.

The earliest occurrence that I have found of the phrase gaiety of nations used without explicit reference to Samuel Johnson’s remark on David Garrick’s death is from the introduction to An Account of John O’Keefe, Esq. ⁵ [With a Portrait of Him.], an unsigned article written for, and published in, The European Magazine, and London Review (London, England) of July 1788:

If to have illumined the gaiety of nations, and to have increased the publick stock of harmless pleasure, without contaminating the mind and without seducing the imagination, are circumstances which deserve applause, and intitle any person to the acknowledgments of mankind, the Gentleman whose portrait ornaments the present Magazine, will be thought of by posterity with kindness, and by his contemporaries with approbation.

⁵ John O’Keefe (1747-1833) was an Irish actor and playwright.

The English essayist, critic and philosopher William Hazlitt (1778-1830) jocularly echoed Samuel Johnson’s phrase in On Actors and Acting, published in The Round Table: A Collection of Essays on Literature, Men, and Manners (Edinburgh: Archibald Constable and Co. – London: Longman, Hurst, Rees, Orme, and Brown – 1817):

Mr Kean is an excellent substitute for the memory of Garrick, whom we never saw. When an author dies, it is no matter, for his works remain. When a great actor dies, there is a void produced in society, a gap which requires to be filled up. Who does not go to see Kean? Who, if Garrick were alive, would go to see him? At least, one or the other must have quitted the stage.—We have seen what a ferment has been excited among our living artists by the exhibition of the works of the old Masters at the British Gallery. What would the actors say to it, if, by any spell or power of necromancy, all the celebrated actors, for the last hundred years, could be made to appear again on the boards of Covent-Garden and Drury-Lane, for the last time, in all their most brilliant parts? What a rich treat to the town, what a feast for the critics, to go and see Betterton, and Booth, and Wilks, and Sandford, and Nokes, and Leigh, and Penkethman, and Bullock, and Estcourt, and Dogget, and Mrs Barry, and Mrs Montfort, and Mrs Oldfield, and Mrs Bracegirdle, and Mrs Gibber, and Gibber himself, the prince of coxcombs, and Macklin, and Quin, and Rich, and Mrs Clive, and Mrs Pritchard, and Mrs Abington, and Weston, and Shuter, and Garrick, and all the rest of those, who “gladdened life, and whose deaths eclipsed the gaiety of nations!”