The following quotation appears in which work?

"'How long,' they say, 'how long, O cruel nation,
Will you stand, to move the world, on a child's heart,—
Stifle down with a mailed heel its palpitation,
And tread onward to your throne amid the mart?
Our blood splashes upward, O our tyrants,
And your purple shews your path;
But the child's sob curseth deeper in the silence
Than the strong man in his wrath!'"