it seems to be Thomas Carlyle in Critical and Miscellaneous Essays.
Google books has it. I copied this much (from pp 218-219):
It used to be said that lions do not paint, that poor men do
not write; but the case is altering now. Here is a voice
coming from the deep Cyclopean forges, where Labour, in
real soot and sweat, beats with his thousand hammers ' the red son of the furnace;' doing personal battle with Necessity, and her dark brute Powers, to make them reasonable and serviceable ; an intelligible voice from the hitherto Mute and Irrational, to tell us at first hand how it is with him, what in very deed is the theorem of the world and of himself, which he, in those dim depths of his, in that wearied head of his, has put together. To which voice, in several respects significant enough, let good ear be given.