In American Notes, 1842, by Charles Dickens, full text available in Project Gutenberg,
http://www.gutenberg.org/ebooks/675
"I believe that very few men are
capable of estimating the immense amount of torture and agony which this
dreadful punishment, prolonged for years, inflicts upon the sufferers; and in
guessing at it myself, and in reasoning from what I have seen written upon
their faces, and what to my certain knowledge they feel within, I am only the
more convinced that there is a depth of terrible endurance in which none but
the sufferers themselves can fathom, and which no man has a right to inflict
upon his fellow creature. I hold this slow and daily tampering with the
mysteries of the brain to be immeasurably worse than any torture of the body;
and because its ghastly signs and tokens are not so palpable to the eye and
sense of touch as scars upon the flesh; because its wounds are not upon the
surface, and it extorts few cries that human ears can hear; therefore the more
I denounce it, as a secret punishment which slumbering humanity is not roused
up to stay."
