“Love is a clash of lightnings”

Source: The Roominghouse Madrigals: Early Selected Poems, 1946-1966

Act IV, scene i.
Aminta (1573)

Source: E Pluribus Unicorn

The Golden Violet - The Child of the Sea
The Golden Violet (1827)

Letter to George Bainton, 15 October 1888, solicited for and printed in George Bainton, The Art of Authorship: Literary Reminiscences, Methods of Work, and Advice to Young Beginners (1890), pp. 87–88 http://books.google.com/books?id=XjBjzRN71_IC&pg=PA87.
Twain repeated the lightning bug/lightning comparison in several contexts, and credited Josh Billings for the idea:
Josh Billings defined the difference between humor and wit as that between the lightning bug and the lightning.
Speech at the 145th annual dinner of St. Andrew's Society, New York, 30 November 1901, Mark Twain Speaking (1976), ed. Paul Fatout, p. 424
Billings' original wording was characteristically affected:
Don't mistake vivacity for wit, thare iz about az mutch difference az thare iz between lightning and a lightning bug.
Josh Billings' Old Farmer's Allminax, "January 1871" http://books.google.com/books?id=sUI1AAAAMAAJ&pg=PT30. Also in Everybody's Friend, or; Josh Billing's Encyclopedia and Proverbial Philosophy of Wit and Humor (1874), p. 304 http://books.google.com/books?id=7rA8AAAAYAAJ&pg=PA304
Source: The Wit and Wisdom of Mark Twain

Lyrics of "Loved by the Sun", on the soundtrack of the film Legend (1986).

Act iv, Scene v
Every Man in His Humour (1598)

Josh Billings' Old Farmer's Allminax, "January 1871" http://books.google.com/books?id=sUI1AAAAMAAJ&q=%22Don't+mistake+vivacity+for+wit+thare+iz+about+az+mutch+difference+az+thare+iz+between+lightning+and+a+lightning+bug%22&pg=PT30#v=onepage (1870)

Black Elk Speaks (1961)