This poem by Strickland Gillilan (1869-1954) from his 1917 anthology Including Finnigan is, according to J. Walter Wilson in Verbatim, the source of the English phrase "off again, on again." (Xrefer's entry from The American Heritage Dictionary of Idioms says only that the phrase comes from railroad accidents, as it is used here in the poem.) It's also a good example of the use of dialect in nineteenth-century American humor; the spelling of the words represents the Irish accents of the two men chronicled.
Superintindint was Flannigan;
Boss av th' siction wuz Finnigin.
Whiniver th' cyars got off th' thrack
An' muddled up things t' th' divvle an' back,
Finnigin writ it t' Flannigan,
Afther th' wrick wuz all on agin;
That is, this Finnigin
Repoorted t' Flannigan.
Whin Finnigin furrst writ t' Flannigan,
He writed tin pa-ages, did Finnigin;
An' he towld just how th' wrick occurred--
Yis, minny a tajus, blundherin' wurrd
Did Finnigin write t' Flannigan
After th' cyars had gone on agin--
That's th' way Finnigin
Repoorted t' Flannigan.
Now Flannigan knowed more than Finnigin--
He'd more idjucation, had Flannigan.
An' ut wore 'm clane an' complately out
T' tell what Finnigin writ about
In 's writin' t' Musther Flannigan.
So he writed this back. "Musther Finnigin--
Don't do sich a sin agin;
Make 'em brief, Finnigin!"
Whin Finnigin got that frum Flannigan
He blushed rosy-red, did Finnigin.
An' he said: "I'll gamble a whole month's pay
That ut'll be minny an' minny a day
Befure sup'rintindint--that's Flannigan--
Gits a whack at that very same sin agin.
Frum Finnigin to Flannigan
Repoorts won't be loong agin."
Wan day on th' siction av Finnigin,
On th' road sup'rintinded be Flannigan,
A ra-ail give way on a bit av a curve
An' some cyars wint off as they made th' shwarrve.
"They's nobody hurted," says Finnigin,
"But repoorts must be made t' Flannigan."
An' be winked at McGorrigan
Who married a Finnigin.
He was shantyin' thin, suz Finnigin,
As minny a railroader's been agin,
An' 'is shmokey ol' lamp wuz burnin' bright
In Finnigin' shanty all that night--
Bilin' down 's repoort, wuz Finnigin.
An' he writed this here: "Musther Flannigan:--
Off agin, on agin,
Gone agin.--Finnigin."

J. Walter Wilson, "On Again, Off Again, Finnegan," Verbatim: from the bawdy to the sublime, the best writing on language for word lovers, grammar mavens, and armchair linguists. Erin McKean, ed. San Diego: Harcourt, Inc, 2001.