As posted by Escamilo, the song was written originally by G. Turco with music by Luigi Denza, 1880.
Will S. Rising first made it a hit in 1885 in New York, with a version called "Jammo! Onward Let Us Go," published by Willis Woodward and Co., NY, and written by Sidney Rosenfeld.

Rosenfeld's words, as sung by Rising, are given in pdmusic: Jammo
Public Domain Music gives the English revision (three verses) and the Neopolitan original.

Chorus:
Jammo Jammo, Onward let us go,
Jammo Jammo, Upward let us go,
Funiculi, funicula,
Funiculi, funicula,
Ncoppa jammo ja "Funiculi, funicula."
(pronounded yammo)
This may be posted in another of the threads.