I knew that I had gained — A Tale of Two Cities

I knew that I had gained ¹
And yet I knew not how
By Diminution it was not
But Discipline unto

A Rigor unrelieved ⁵
Except by the Content
Another bear its Duplicate
In other Continent.

(F.1033/J.1022)

[1–8]:: This poem talks about Sydney Carton and Charles Darney in A Tale of Two Cities (1859) by Charles Dickens.
[1] I had gained:: Charles Darney, who gained his life at the end.
[2] knew not how:: Darney was drugged in the process.
[3] Diminution:: Darney was not willing to be saved in that way.
[4] Discipline unto:: Darney was half forced, under discipline of Carton.
[5] Rigor unrelieved:: the death execution.
[6] Except, Content:: Carton died willingly.
[7] Duplicate:: the two men looked alike.
[8] other Continent:: Paris and London.